integrate.h

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/*
 * Copyright (c) 2011-2015:  G-CSC, Goethe University Frankfurt
 * Author: Andreas Vogel
 * 
 * This file is part of UG4.
 * 
 * UG4 is free software: you can redistribute it and/or modify it under the
 * terms of the GNU Lesser General Public License version 3 (as published by the
 * Free Software Foundation) with the following additional attribution
 * requirements (according to LGPL/GPL v3):
 * 
 * (1) The following notice must be displayed in the Appropriate Legal Notices
 * of covered and combined works: "Based on UG4 (www.ug4.org/license)".
 * 
 * (2) The following notice must be displayed at a prominent place in the
 * terminal output of covered works: "Based on UG4 (www.ug4.org/license)".
 * 
 * (3) The following bibliography is recommended for citation and must be
 * preserved in all covered files:
 * "Reiter, S., Vogel, A., Heppner, I., Rupp, M., and Wittum, G. A massively
 *   parallel geometric multigrid solver on hierarchically distributed grids.
 *   Computing and visualization in science 16, 4 (2013), 151-164"
 * "Vogel, A., Reiter, S., Rupp, M., Nägel, A., and Wittum, G. UG4 -- a novel
 *   flexible software system for simulating pde based models on high performance
 *   computers. Computing and visualization in science 16, 4 (2013), 165-179"
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Lesser General Public License for more details.
 */
 
#ifndef __H__UG__LIB_DISC__FUNCTION_SPACES__INTEGRATE__
#define __H__UG__LIB_DISC__FUNCTION_SPACES__INTEGRATE__
 
#include <cmath>
 
#include <boost/function.hpp>
 
#include "common/common.h"
 
#include "lib_grid/tools/subset_group.h"
 
#include "lib_disc/common/function_group.h"
#include "lib_disc/common/groups_util.h"
#include "lib_disc/domain_util.h"  // for CollectCornerCoordinates
#include "lib_disc/quadrature/quadrature_provider.h"
#include "lib_disc/local_finite_element/local_finite_element_provider.h"
#include "lib_disc/spatial_disc/disc_util/fv1_geom.h"
#include "lib_disc/spatial_disc/user_data/user_data.h"
#include "lib_disc/spatial_disc/user_data/const_user_data.h"
#include "lib_disc/reference_element/reference_mapping_provider.h"
 
#ifdef UG_FOR_LUA
#include "bindings/lua/lua_user_data.h"
#endif
 
namespace ug{
 
 
// Object encapsulating (scalar) GridFunction related data
template <typename TGridFunction>
class ScalarGridFunctionData
{
public:
  typedef typename TGridFunction::domain_type domain_type;
 
  ScalarGridFunctionData(TGridFunction& gridFct, size_t cmp)
  : m_gridFct(gridFct), m_fct(cmp),
   m_id(m_gridFct.local_finite_element_id(m_fct))
  {}
 
  TGridFunction& grid_function()
  {return  m_gridFct;}
 
  const TGridFunction& grid_function() const
  {return  m_gridFct;}
 
  size_t fct()
  {return m_fct;}
 
  const LFEID &id() const
  {return m_id;}
 
  bool is_def_in_subset(int si) const
  { return m_gridFct.is_def_in_subset(m_fct, si); }
 
  SmartPtr<domain_type> domain() {return m_gridFct.domain();}
 
  ConstSmartPtr<domain_type> domain() const {return m_gridFct.domain();}
 
  template <typename TElem>
  size_t dof_indices(TElem* elem, std::vector<DoFIndex>& ind, bool bHang = false, bool bClear = true) const
  {return m_gridFct.dof_indices(elem, m_fct, ind, bHang, bClear);}
 
private:
    TGridFunction& m_gridFct;
 
    size_t m_fct;
 
    LFEID m_id;
};
 
// Integrand Interface
 
 
 
template <typename TData, int TWorldDim>
class IIntegrand
{
  public:
    static const int worldDim = TWorldDim;
 
    typedef TData data_type;
 
 
    virtual void values(TData vValue[],
                        const MathVector<worldDim> vGlobIP[],
                        GridObject* pElem,
                          const MathVector<worldDim> vCornerCoords[],
                        const MathVector<1> vLocIP[],
                        const MathMatrix<1, worldDim> vJT[],
                        const size_t numIP) = 0;
    virtual void values(TData vValue[],
                        const MathVector<worldDim> vGlobIP[],
                        GridObject* pElem,
                          const MathVector<worldDim> vCornerCoords[],
                        const MathVector<2> vLocIP[],
                        const MathMatrix<2, worldDim> vJT[],
                        const size_t numIP) = 0;
    virtual void values(TData vValue[],
                        const MathVector<worldDim> vGlobIP[],
                        GridObject* pElem,
                          const MathVector<worldDim> vCornerCoords[],
                        const MathVector<3> vLocIP[],
                        const MathMatrix<3, worldDim> vJT[],
                        const size_t numIP) = 0;
 
    virtual ~IIntegrand() {}
 
 
    virtual void set_subset(int si) {m_si = si;}
 
    inline int subset() const {return m_si;}
  
    protected:
    int m_si;
};
 
template <typename TData, int TWorldDim, typename TImpl>
class StdIntegrand : public IIntegrand<TData, TWorldDim>
{
  public:
    static const int worldDim = TWorldDim;
 
    typedef TData data_type;
 
    virtual void values(TData vValue[],
                        const MathVector<worldDim> vGlobIP[],
                        GridObject* pElem,
                          const MathVector<worldDim> vCornerCoords[],
                        const MathVector<1> vLocIP[],
                        const MathMatrix<1, worldDim> vJT[],
                        const size_t numIP)
    {
      getImpl().template evaluate<1>(vValue,vGlobIP,pElem,vCornerCoords,vLocIP,vJT,numIP);
    }
    virtual void values(TData vValue[],
                        const MathVector<worldDim> vGlobIP[],
                        GridObject* pElem,
                          const MathVector<worldDim> vCornerCoords[],
                        const MathVector<2> vLocIP[],
                        const MathMatrix<2, worldDim> vJT[],
                        const size_t numIP)
    {
      getImpl().template evaluate<2>(vValue,vGlobIP,pElem,vCornerCoords,vLocIP,vJT,numIP);
    }
    virtual void values(TData vValue[],
                        const MathVector<worldDim> vGlobIP[],
                        GridObject* pElem,
                          const MathVector<worldDim> vCornerCoords[],
                        const MathVector<3> vLocIP[],
                        const MathMatrix<3, worldDim> vJT[],
                        const size_t numIP)
    {
      getImpl().template evaluate<3>(vValue,vGlobIP,pElem,vCornerCoords,vLocIP,vJT,numIP);
    }
    
  protected:
    TImpl& getImpl() {return static_cast<TImpl&>(*this);}
 
    const TImpl& getImpl() const {return static_cast<const TImpl&>(*this);}
};
 
// Generic Volume Integration Routine
 
 
template <int WorldDim, int dim, typename TConstIterator>
number Integrate(TConstIterator iterBegin,
                 TConstIterator iterEnd,
                 typename domain_traits<WorldDim>::position_accessor_type& aaPos,
                 IIntegrand<number, WorldDim>& integrand,
                 int quadOrder, std::string quadType,
                 Grid::AttachmentAccessor<
                  typename domain_traits<dim>::grid_base_object, ANumber>
                  *paaElemContribs = NULL
                 )
{
  PROFILE_FUNC();
 
//  reset the result
  number integral = 0.0;
 
//  note: this iterator is for the base elements, e.g. Face and not
//      for the special type, e.g. Triangle, Quadrilateral
  TConstIterator iter = iterBegin;
 
//  this is the base element type (e.g. Face). This is the type when the
//  iterators above are dereferenciated.
  typedef typename domain_traits<dim>::grid_base_object grid_base_object;
 
//  get quad type
  if(quadType.empty()) quadType = "best";
  QuadType type = GetQuadratureType(quadType);
 
//  accessing without dereferencing a pointer first is simpler...
  Grid::AttachmentAccessor<grid_base_object, ANumber> aaElemContribs;
  if(paaElemContribs)
    aaElemContribs = *paaElemContribs;
 
//  We'll reuse containers to avoid reallocations
  std::vector<MathVector<WorldDim> > vCorner;
  std::vector<MathVector<WorldDim> > vGlobIP;
  std::vector<MathMatrix<dim, WorldDim> > vJT;
  std::vector<number> vValue;
 
//  iterate over all elements
  for(; iter != iterEnd; ++iter)
  {
  //  get element
    grid_base_object* pElem = *iter;
 
  //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
    ReferenceObjectID roid = (ReferenceObjectID) pElem->reference_object_id();
 
  //  get quadrature Rule for reference object id and order
    try{
    const QuadratureRule<dim>& rQuadRule
          = QuadratureRuleProvider<dim>::get(roid, quadOrder, type);
 
  //  get reference element mapping by reference object id
    DimReferenceMapping<dim, WorldDim>& mapping
              = ReferenceMappingProvider::get<dim, WorldDim>(roid);
 
  //  number of integration points
    const size_t numIP = rQuadRule.size();
 
  //  get all corner coordinates
    CollectCornerCoordinates(vCorner, *pElem, aaPos, true);
 
  //  update the reference mapping for the corners
    mapping.update(&vCorner[0]);
 
  //  compute global integration points
    vGlobIP.resize(numIP);
    mapping.local_to_global(&(vGlobIP[0]), rQuadRule.points(), numIP);
 
  //  compute transformation matrices
    vJT.resize(numIP);
    mapping.jacobian_transposed(&(vJT[0]), rQuadRule.points(), numIP);
 
  //  compute integrand values at integration points
    vValue.resize(numIP);
    try
    {
      integrand.values(&(vValue[0]), &(vGlobIP[0]),
                       pElem, &vCorner[0], rQuadRule.points(),
               &(vJT[0]),
               numIP);
    }
    UG_CATCH_THROW("Unable to compute values of integrand at integration point.");
 
  //  reset contribution of this element
    number intValElem = 0;
 
  //  loop integration points
    for(size_t ip = 0; ip < numIP; ++ip)
    {
    //  get quadrature weight
      const number weightIP = rQuadRule.weight(ip);
 
    //  get determinate of mapping
      const number det = SqrtGramDeterminant(vJT[ip]);
 
    //  add contribution of integration point
      intValElem += vValue[ip] * weightIP * det;
    }
 
  //  add to global sum
    integral += intValElem;
    if(aaElemContribs.valid())
      aaElemContribs[pElem] = intValElem;
 
    }UG_CATCH_THROW("SumValuesOnElems failed.");
  } // end elem
 
//  return the summed integral contributions of all elements
  return integral;
}
 
template <typename TGridFunction, int dim>
number IntegrateSubset(IIntegrand<number, TGridFunction::dim> &spIntegrand,
                       TGridFunction& spGridFct,
                       int si, int quadOrder, std::string quadType)
{
//  integrate elements of subset
  typedef typename TGridFunction::template dim_traits<dim>::grid_base_object grid_base_object;
  typedef typename TGridFunction::template dim_traits<dim>::const_iterator const_iterator;
 
  spIntegrand.set_subset(si);
  
  return Integrate<TGridFunction::dim,dim,const_iterator>
          (spGridFct.template begin<grid_base_object>(si),
                   spGridFct.template end<grid_base_object>(si),
           spGridFct.domain()->position_accessor(),
                   spIntegrand,
                   quadOrder, quadType);
}
 
 
template <typename TGridFunction>
number IntegrateSubsets(IIntegrand<number, TGridFunction::dim> &spIntegrand,
                        TGridFunction& spGridFct,
                        const char* subsets, int quadOrder,
                        std::string quadType = std::string())
{
//  world dimensions
  static const int dim = TGridFunction::dim;
 
//  read subsets
  SubsetGroup ssGrp(spGridFct.domain()->subset_handler());
  if(subsets != NULL)
  {
    ssGrp.add(TokenizeString(subsets));
    UG_COND_THROW(!SameDimensionsInAllSubsets(ssGrp), "IntegrateSubsets: Subsets '"<<subsets<<"' do not have same dimension."
               "Cannot integrate on subsets of different dimensions.");
    UG_LOG("IntegrateSubsets for subsets="<<subsets<<"\n");
  }
  else
  {
  //  add all subsets and remove lower dim subsets afterwards
    ssGrp.add_all();
    RemoveLowerDimSubsets(ssGrp);
  }
 
//  reset value
  number value = 0;
 
//  loop subsets
  for(size_t i = 0; i < ssGrp.size(); ++i)
  {
  //  get subset index
    const int si = ssGrp[i];
 
  //  check dimension
  UG_COND_THROW(ssGrp.dim(i) > dim, "IntegrateSubsets: Dimension of subset is "<<ssGrp.dim(i)<<", but "
            " world dimension is "<<dim<<". Cannot integrate this.");
 
  //  integrate elements of subset
    try{
    switch(ssGrp.dim(i))
    {
      case DIM_SUBSET_EMPTY_GRID: break;
      case 1: value += IntegrateSubset<TGridFunction, 1>(spIntegrand, spGridFct, si, quadOrder, quadType); break;
      case 2: value += IntegrateSubset<TGridFunction, 2>(spIntegrand, spGridFct, si, quadOrder, quadType); break;
      case 3: value += IntegrateSubset<TGridFunction, 3>(spIntegrand, spGridFct, si, quadOrder, quadType); break;
      default: UG_THROW("IntegrateSubsets: Dimension "<<ssGrp.dim(i)<<" not supported. "
                        " World dimension is "<<dim<<".");
    }
    }
    UG_CATCH_THROW("IntegrateSubsets: Integration failed on subset "<<si);
  }
 
#ifdef UG_PARALLEL
  // sum over processes
  if(pcl::NumProcs() > 1)
  {
    pcl::ProcessCommunicator com;
    number local = value;
    com.allreduce(&local, &value, 1, PCL_DT_DOUBLE, PCL_RO_SUM);
  }
#endif
 
//  return the result
  return value;
}
 
 
// UserData Integrand
 
template <typename TData, typename TGridFunction>
class UserDataIntegrand
  : public StdIntegrand<TData, TGridFunction::dim, UserDataIntegrand<TData, TGridFunction> >
{
  public:
  //  world dimension of grid function
    static const int worldDim = TGridFunction::dim;
 
  //  data type
    typedef TData data_type;
 
  private:
  //  data to integrate
    SmartPtr<UserData<TData, worldDim> > m_spData;
 
  //  grid function
    TGridFunction* m_spGridFct;
 
  //  time
    number m_time;
 
  public:
    UserDataIntegrand(SmartPtr<UserData<TData, worldDim> > spData,
                          TGridFunction* spGridFct,
                          number time)
    : m_spData(spData), m_spGridFct(spGridFct), m_time(time)
    {
      m_spData->set_function_pattern(spGridFct->function_pattern());
    };
 
    UserDataIntegrand(SmartPtr<UserData<TData, worldDim> > spData,
                number time)
    : m_spData(spData), m_spGridFct(NULL), m_time(time)
    {
      UG_COND_THROW(m_spData->requires_grid_fct(),
            "UserDataIntegrand: Missing GridFunction, but data requires grid function.");
    };
 
    template <int elemDim>
    void evaluate(TData vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
    //  get local solution if needed
      if(m_spData->requires_grid_fct())
      {
      //  create storage
        LocalIndices ind;
        LocalVector u;
 
      //  get global indices
        m_spGridFct->indices(pElem, ind);
 
      //  adapt local algebra
        u.resize(ind);
 
      //  read local values of u
        GetLocalVector(u, *m_spGridFct);
 
      //  compute data
        try{
          (*m_spData)(vValue, vGlobIP, m_time, this->m_si, pElem,
                vCornerCoords, vLocIP, numIP, &u, &vJT[0]);
        }
        UG_CATCH_THROW("UserDataIntegrand: Cannot evaluate data.");
      }
      else
      {
      //  compute data
        try{
          (*m_spData)(vValue, vGlobIP, m_time, this->m_si, numIP);
        }
        UG_CATCH_THROW("UserDataIntegrand: Cannot evaluate data.");
      }
 
    }
};
 
 
 
 
template <typename TData, typename TGridFunction>
class UserDataIntegrandSq
  : public StdIntegrand<number, TGridFunction::dim, UserDataIntegrandSq<TData, TGridFunction> >
{
  public:
  //  world dimension of grid function
    static const int worldDim = TGridFunction::dim;
 
  //  data type
    typedef TData data_type;
 
  private:
  //  data to integrate
    SmartPtr<UserData<TData, worldDim> > m_spData;
 
  //  grid function
    const TGridFunction* m_pGridFct;
 
  //  time
    number m_time;
 
  public:
    UserDataIntegrandSq(SmartPtr<UserData<TData, worldDim> > spData,
                          const TGridFunction* pGridFct,
                          number time)
    : m_spData(spData), m_pGridFct(pGridFct), m_time(time)
    {
      m_spData->set_function_pattern(pGridFct->function_pattern());
    };
 
    UserDataIntegrandSq(SmartPtr<UserData<TData, worldDim> > spData,
                number time)
    : m_spData(spData), m_pGridFct(NULL), m_time(time)
    {
      if(m_spData->requires_grid_fct())
        UG_THROW("UserDataIntegrand: Missing GridFunction, but "
            " data requires grid function.")
    };
 
    
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
 
      std::vector<TData> tmpValues(numIP);
 
    //  get local solution if needed
      if(m_spData->requires_grid_fct())
      {
        UG_ASSERT(m_pGridFct!=NULL, "Error: Requires valid pointer!")
      //  create storage
        LocalIndices ind;
        LocalVector u;
 
      //  get global indices
        m_pGridFct->indices(pElem, ind);
 
      //  adapt local algebra
        u.resize(ind);
 
      //  read local values of u
        GetLocalVector(u, *m_pGridFct);
 
      //  compute data
        try{
          (*m_spData)(&tmpValues.front(), vGlobIP, m_time, this->m_si, pElem,
                vCornerCoords, vLocIP, numIP, &u, &vJT[0]);
        }
        UG_CATCH_THROW("UserDataIntegrand: Cannot evaluate data.");
      }
      else
      {
      //  compute data
        try{
          (*m_spData)(&tmpValues.front(), vGlobIP, m_time, this->m_si, numIP);
        }
        UG_CATCH_THROW("UserDataIntegrand: Cannot evaluate data.");
      }
 
      for (size_t i=0; i<numIP; ++i)
      {
        vValue[i]=inner_prod(tmpValues[i], tmpValues[i]);
      }
 
    }
  protected:
 
    number inner_prod(const number &d1, const number &d2)
    {return d1*d2;}
 
    number inner_prod(const MathVector<worldDim> &d1, const MathVector<worldDim> &d2)
    {return VecDot(d1, d2);}
 
    template<typename T>
    number inner_prod(const T &d1, const T &d2)
    { UG_ASSERT(0, "NOT IMPLEMENTED"); return 0.0;}
};
 
 
 
 
template <typename TData, typename TGridFunction>
class UserDataDistIntegrandSq
    : public StdIntegrand<number, TGridFunction::dim, UserDataDistIntegrandSq<TData, TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
    // typedef typename L2Integrand<TGridFunction>::weight_type weight_type;
 
  protected:
    ScalarGridFunctionData<TGridFunction> m_fineData;
    const int m_fineTopLevel;
 
    ScalarGridFunctionData<TGridFunction> m_coarseData;
    const int m_coarseTopLevel;
 
    SmartPtr<MultiGrid> m_spMG;
 
 
 
    SmartPtr<UserData<TData, worldDim> > m_spData;
    // ConstSmartPtr<weight_type> m_spWeight;
 
    double m_time;
  public:
 
    UserDataDistIntegrandSq(SmartPtr<UserData<TData, worldDim> > spData, TGridFunction& fineGridFct, size_t fineCmp,
          TGridFunction& coarseGridFct, size_t coarseCmp)
    : m_fineData(fineGridFct, fineCmp), m_fineTopLevel(fineGridFct.dof_distribution()->grid_level().level()),
      m_coarseData(coarseGridFct, coarseCmp), m_coarseTopLevel(coarseGridFct.dof_distribution()->grid_level().level()),
      m_spMG(m_fineData.domain()->grid()), m_spData(spData), m_time(0.0) /*, m_spWeight(make_sp(new ConstUserNumber<TGridFunction::dim>(1.0)))*/
    {
      if(m_fineTopLevel < m_coarseTopLevel)
        UG_THROW("UserDataDistIntegrandSq: fine and top level inverted.");
 
      if(m_fineData.domain().get() != m_coarseData.domain().get())
        UG_THROW("UserDataDistIntegrandSq: grid functions defined on different domains.");
    };
 
    virtual ~UserDataDistIntegrandSq() {}
 
    virtual void set_subset(int si)
    {
      if(!m_fineData.is_def_in_subset(si))
        UG_THROW("UserDataDistIntegrandSq: Grid function component"
            <<m_fineData.fct()<<" not defined on subset "<<si);
      if(!m_coarseData.is_def_in_subset(si))
        UG_THROW("UserDataDistIntegrandSq: Grid function component"
            <<m_coarseData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pFineElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vFineLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
 
 
    // must return 0.0, if m_spData is independent of grid functions
      if(!m_spData->requires_grid_fct()) {
        for (size_t i=0; i<numIP; ++i) { vValue[i]=0.0; }
        return;
      }
 
    //  get coarse element
      GridObject* pCoarseElem = pFineElem;
      if(m_coarseTopLevel < m_fineTopLevel){
        int parentLevel = m_spMG->get_level(pCoarseElem);
        while(parentLevel > m_coarseTopLevel){
          pCoarseElem = m_spMG->get_parent(pCoarseElem);
          parentLevel = m_spMG->get_level(pCoarseElem);
        }
      }
 
    //  get corner coordinates
      typedef typename TGridFunction::template dim_traits<elemDim>::grid_base_object TElem;
      std::vector<MathVector<worldDim> > vCornerCoarse;
      CollectCornerCoordinates(vCornerCoarse, *static_cast<TElem*>(pCoarseElem), *m_coarseData.domain());
 
    //  get Reference Mapping
      const ReferenceObjectID coarseROID = pCoarseElem->reference_object_id();
      DimReferenceMapping<elemDim, worldDim>& map
        = ReferenceMappingProvider::get<elemDim, worldDim>(coarseROID, vCornerCoarse);
 
      std::vector<MathVector<elemDim> > vCoarseLocIP;
      vCoarseLocIP.resize(numIP);
      for(size_t ip = 0; ip < vCoarseLocIP.size(); ++ip) VecSet(vCoarseLocIP[ip], 0.0);
      map.global_to_local(&vCoarseLocIP[0], vGlobIP, numIP);
 
    // element weights
    /*  typedef typename weight_type::data_type ipdata_type;
      std::vector<ipdata_type> fineElemWeights(numIP, 1.0);
      UG_ASSERT(m_spWeight.valid(), "L2DistIntegrand::evaluate requires valid weights! ");
      (*m_spWeight)(&fineElemWeights[0], vFineGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), numIP);*/
 
 
    //  get trial space
    /*  const LocalShapeFunctionSet<elemDim>& rFineLSFS =
          LocalFiniteElementProvider::get<elemDim>(fineROID, m_fineData.id());
      const LocalShapeFunctionSet<elemDim>& rCoarseLSFS =
          LocalFiniteElementProvider::get<elemDim>(coarseROID, m_coarseData.id());*/
 
    //  get multiindices of element
      /*std::vector<DoFIndex> vFineMI, vCoarseMI;
      m_fineData.dof_indices(pFineElem, vFineMI);
      m_coarseData.dof_indices(pCoarseElem, vCoarseMI);*/
 
      TData fineValues[numIP];
      TData coarseValues[numIP];
 
 
 
    //  compute coarse data
      try{
        LocalVector uCoarse;
        LocalIndices indCoarse;
 
        m_coarseData.grid_function().indices(pCoarseElem, indCoarse);
        uCoarse.resize(indCoarse);
        GetLocalVector(uCoarse, m_coarseData.grid_function());
 
        (*m_spData)(coarseValues, vGlobIP, m_time, this->m_si, pCoarseElem,
            &vCornerCoarse[0], &vCoarseLocIP[0], numIP, &uCoarse, &vJT[0]);
      } UG_CATCH_THROW("UserDataDistIntegrandSq: Cannot evaluate coarse data.");
 
 
    //  compute fine data
      try{
        LocalVector uFine;
        LocalIndices indFine;
 
        m_fineData.grid_function().indices(pFineElem, indFine);
        uFine.resize(indFine);
        GetLocalVector(uFine, m_fineData.grid_function());
 
        (*m_spData)(fineValues, vGlobIP, m_time, this->m_si, pFineElem,
            vCornerCoords, vFineLocIP, numIP, &uFine, &vJT[0]);
      } UG_CATCH_THROW("UserDataDistIntegrandSq: Cannot evaluate fine data.");
 
    //  loop all integration points
      for(size_t ip = 0; ip < numIP; ++ip)
      {
        vValue[ip] = inner_dist2(fineValues[ip], coarseValues[ip]);
      }
 
    }
 
 
  protected:
 
      number inner_prod(const number &d1, const number &d2)
      {return d1*d2;}
 
      number inner_prod(const MathVector<worldDim> &d1, const MathVector<worldDim> &d2)
      {return VecDot(d1, d2);}
 
      template<typename T>
      number inner_prod(const T &d1, const T &d2)
      { UG_ASSERT(0, "NOT IMPLEMENTED"); return 0.0;}
 
 
 
      number inner_dist2(const number &v1, const number &v2)
      { return (v1-v2)*(v1-v2); }
 
      number inner_dist2(const MathVector<worldDim> &v1, const MathVector<worldDim> &v2)
      { return VecDistanceSq(v1, v2); }
 
      template<typename T>
      number inner_dist2(const T &d1, const T &d2)
      { UG_ASSERT(0, "NOT IMPLEMENTED"); return 0.0;}
 
};
 
 
// Volume Integrand implementations
 
template <typename TGridFunction>
number Integral(SmartPtr<UserData<number, TGridFunction::dim> > spData,
                TGridFunction& spGridFct,
                const char* subsets, number time,
                int quadOrder, std::string quadType)
{
  UserDataIntegrand<number, TGridFunction> spIntegrand(spData, &spGridFct, time);
  return IntegrateSubsets(spIntegrand, spGridFct, subsets, quadOrder, quadType);
}
 
template <typename TGridFunction>
number Integral(SmartPtr<UserData<number, TGridFunction::dim> > spData, SmartPtr<TGridFunction> spGridFct,
                const char* subsets, number time, int quadOrder, std::string quadType)
{ return Integral(spData, *spGridFct, subsets, time, quadOrder, quadType); }
 
template <typename TGridFunction>
number Integral(SmartPtr<UserData<number, TGridFunction::dim> > spData, SmartPtr<TGridFunction> spGridFct,const char* subsets,number time, int order)
{return Integral(spData, spGridFct, subsets, time, order, "best");}
 
template <typename TGridFunction>
number Integral(SmartPtr<UserData<number, TGridFunction::dim> > spData, SmartPtr<TGridFunction> spGridFct,const char* subsets,number time)
{return Integral(spData, spGridFct, subsets, time, 1, "best");}
 
template <typename TGridFunction>
number Integral(SmartPtr<UserData<number, TGridFunction::dim> > spData, SmartPtr<TGridFunction> spGridFct,number time)
{return Integral(spData, spGridFct, NULL, time, 1, "best");}
 
template <typename TGridFunction>
number Integral(SmartPtr<UserData<number, TGridFunction::dim> > spData, SmartPtr<TGridFunction> spGridFct,const char* subsets)
{return Integral(spData, spGridFct, subsets, 0.0, 1, "best");}
 
template <typename TGridFunction>
number Integral(SmartPtr<UserData<number, TGridFunction::dim> > spData, SmartPtr<TGridFunction> spGridFct)
{return Integral(spData, spGridFct, NULL, 0.0, 1, "best");}
 
// const data
 
template <typename TGridFunction>
number Integral(number val, SmartPtr<TGridFunction> spGridFct,
                const char* subsets,
                number time, int quadOrder)
{
  static const int dim = TGridFunction::dim;
  SmartPtr<UserData<number, dim> > sp =
      make_sp(new ConstUserNumber<dim>(val));
  return Integral(sp, spGridFct, subsets, time, quadOrder);
}
 
template <typename TGridFunction>
number Integral(number val, SmartPtr<TGridFunction> spGridFct,const char* subsets,number time)
{return Integral(val, spGridFct, subsets, time, 1);}
 
template <typename TGridFunction>
number Integral(number val, SmartPtr<TGridFunction> spGridFct,number time)
{return Integral(val, spGridFct, NULL, time, 1);}
 
template <typename TGridFunction>
number Integral(number val, SmartPtr<TGridFunction> spGridFct,const char* subsets)
{return Integral(val, spGridFct, subsets, 0.0, 1);}
 
template <typename TGridFunction>
number Integral(number val, SmartPtr<TGridFunction> spGridFct)
{return Integral(val, spGridFct, NULL, 0.0, 1);}
 
// lua data
 
#ifdef UG_FOR_LUA
template <typename TGridFunction>
number Integral(const char* luaFct,
                SmartPtr<TGridFunction> spGridFct,
                const char* subsets, number time,
                int quadOrder, std::string quadType)
{
  static const int dim = TGridFunction::dim;
  SmartPtr<UserData<number, dim> > sp =
      LuaUserDataFactory<number, dim>::create(luaFct);
  return Integral(sp, *spGridFct, subsets, time, quadOrder, quadType);
}
 
template <typename TGridFunction>
number Integral(const char* luaFct, SmartPtr<TGridFunction> spGridFct,const char* subsets,number time, int quadOrder)
{return Integral(luaFct, spGridFct, subsets, time, quadOrder, "best");}
 
template <typename TGridFunction>
number Integral(const char* luaFct, SmartPtr<TGridFunction> spGridFct,const char* subsets,number time)
{return Integral(luaFct, spGridFct, subsets, time, 1, "best");}
 
template <typename TGridFunction>
number Integral(const char* luaFct, SmartPtr<TGridFunction> spGridFct,number time)
{return Integral(luaFct, spGridFct, NULL, time, 1, "best");}
 
template <typename TGridFunction>
number Integral(const char* luaFct, SmartPtr<TGridFunction> spGridFct,const char* subsets)
{return Integral(luaFct, spGridFct, subsets, 0.0, 1, "best");}
 
template <typename TGridFunction>
number Integral(const char* luaFct, SmartPtr<TGridFunction> spGridFct)
{return Integral(luaFct, spGridFct, NULL, 0.0, 1, "best");}
 
#endif
 
 
 
template <typename TGridFunction>
class MaximumDistIntegrand
  : public StdIntegrand<number, TGridFunction::dim, MaximumDistIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
 
  protected:
    ScalarGridFunctionData<TGridFunction> m_scalarData;
 
    double m_max, m_min;
 
  public:
    MaximumDistIntegrand(TGridFunction& gridFct, size_t cmp)
 
    : m_scalarData(gridFct, cmp),
      m_max(-std::numeric_limits<float>::infinity()),
      m_min(std::numeric_limits<float>::infinity())
    {};
 
    virtual ~MaximumDistIntegrand() {};
 
    virtual void set_subset(int si)
    {
      UG_COND_THROW(!m_scalarData.is_def_in_subset(si), "L2ErrorIntegrand: Grid function component" <<
              m_scalarData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    void reset()
    {
      m_min = std::numeric_limits<double>::infinity();
      m_max = -std::numeric_limits<double>::infinity();
    }
 
    double min() { return m_min; }
    double max() { return m_max; }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID roid = pElem->reference_object_id();
 
      try{
        //  get trial space
        const LocalShapeFunctionSet<elemDim>& rTrialSpace =
              LocalFiniteElementProvider::get<elemDim>(roid, m_scalarData.id());
 
        //  number of dofs on element
        const size_t num_sh = rTrialSpace.num_sh();
 
        //  get multiindices of element
        std::vector<DoFIndex> ind;  //  aux. index array
        m_scalarData.dof_indices(pElem, ind);
 
        //  check multi indices
        UG_COND_THROW(ind.size() != num_sh, "L2ErrorIntegrand::evaluate: Wrong number of multi indices.");
 
        //  evaluate function in corners.
        for(size_t sh = 0; sh < num_sh; ++sh)
        {
          //  get value at shape point (e.g. corner for P1 fct)
          const number val = DoFRef(m_scalarData.grid_function(), ind[sh]);
 
          m_max = std::max(m_max, val);
          m_min = std::min(m_min, val);
        }
 
 
      } UG_CATCH_THROW("L2ErrorIntegrand::evaluate: trial space missing.");
    }
};
 
 
template <typename TGridFunction>
number GetMinimum(TGridFunction &gridFct, const char* cmp, const char* subsets)
{
  //  get function id of name & check that function exists
  const size_t fct = gridFct.fct_id_by_name(cmp);
  UG_COND_THROW(fct >= gridFct.num_fct(),
        "L2Error: Function space does not contain a function with name " << cmp << ".");
 
  // Find minimum.
  MaximumDistIntegrand<TGridFunction> spIntegrand(gridFct, fct);
  IntegrateSubsets(spIntegrand, gridFct, subsets, 2);
  return spIntegrand.min();
}
 
template <typename TGridFunction>
number Minimum(SmartPtr<TGridFunction> spGridFct, const char* cmp, const char* subsets)
{ return GetMinimum(*spGridFct, cmp, subsets); }
 
 
// L2 Error Integrand
 
template <typename TGridFunction>
class L2ErrorIntegrand
  : public StdIntegrand<number, TGridFunction::dim, L2ErrorIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
 
  private:
    ScalarGridFunctionData<TGridFunction> m_scalarData;
 
    SmartPtr<UserData<number, worldDim> > m_spExactSolution;
 
    number m_time;
 
  public:
    L2ErrorIntegrand(SmartPtr<UserData<number, worldDim> > spExactSol,
                     TGridFunction& gridFct, size_t cmp,
                     number time)
    : m_scalarData(gridFct, cmp),
      m_spExactSolution(spExactSol), m_time(time)
    {};
 
    virtual ~L2ErrorIntegrand() {};
 
    virtual void set_subset(int si)
    {
      if(!m_scalarData.is_def_in_subset(si))
        UG_THROW("L2ErrorIntegrand: Grid function component"
            <<m_scalarData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID roid = pElem->reference_object_id();
 
      try{
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rTrialSpace =
              LocalFiniteElementProvider::get<elemDim>(roid, m_scalarData.id());
 
    //  number of dofs on element
      const size_t num_sh = rTrialSpace.num_sh();
 
    //  get multiindices of element
      std::vector<DoFIndex> ind;  //  aux. index array
      m_scalarData.dof_indices(pElem, ind);
 
    //  check multi indices
      if(ind.size() != num_sh)
        UG_THROW("L2ErrorIntegrand::evaluate: Wrong number of"
            " multi indices.");
 
    //  loop all integration points
      for(size_t ip = 0; ip < numIP; ++ip)
      {
      //  compute exact solution at integration point
        number exactSolIP;
        (*m_spExactSolution)(exactSolIP, vGlobIP[ip], m_time, this->subset());
 
      //  compute approximated solution at integration point
        number approxSolIP = 0.0;
        for(size_t sh = 0; sh < num_sh; ++sh)
        {
        //  get value at shape point (e.g. corner for P1 fct)
          const number valSH = DoFRef(m_scalarData.grid_function(), ind[sh]);
 
        //  add shape fct at ip * value at shape
          approxSolIP += valSH * rTrialSpace.shape(sh, vLocIP[ip]);
        }
 
      //  get squared of difference
        vValue[ip] = (exactSolIP - approxSolIP);
        vValue[ip] *= vValue[ip];
      }
 
      }
      UG_CATCH_THROW("L2ErrorIntegrand::evaluate: trial space missing.");
    }
};
 
 
 
// L2 Error Integrand
 
 
template <typename TGridFunction>
number L2Error(SmartPtr<UserData<number, TGridFunction::dim> > spExactSol,
               TGridFunction& gridFct, const char* cmp,
               number time, int quadOrder, const char* subsets)
{
//  get function id of name
  const size_t fct = gridFct.fct_id_by_name(cmp);
 
//  check that function exists
  UG_COND_THROW(fct >= gridFct.num_fct(),
        "L2Error: Function space does not contain a function with name " << cmp << ".");
 
  L2ErrorIntegrand<TGridFunction> spIntegrand(spExactSol, gridFct, fct, time);
  return sqrt(IntegrateSubsets(spIntegrand, gridFct, subsets, quadOrder));
}
 
template <typename TGridFunction>
number L2Error(SmartPtr<UserData<number, TGridFunction::dim> > spExactSol,
               SmartPtr<TGridFunction> spGridFct, const char* cmp,
               number time, int quadOrder, const char* subsets)
{ return L2Error(spExactSol, *spGridFct, cmp, time, quadOrder, subsets); }
 
template <typename TGridFunction>
number L2Error(SmartPtr<UserData<number, TGridFunction::dim> > spExactSol,
               SmartPtr<TGridFunction> spGridFct, const char* cmp,
               number time, int quadOrder)
{ return L2Error(spExactSol, *spGridFct, cmp, time, quadOrder, NULL); }
 
 
 
 
#ifdef UG_FOR_LUA
template <typename TGridFunction>
number L2Error(const char* ExactSol,
               SmartPtr<TGridFunction> spGridFct, const char* cmp,
               number time, int quadOrder, const char* subsets)
{
  SmartPtr<UserData<number, TGridFunction::dim> > spExactSol
   = make_sp(new LuaUserData<number, TGridFunction::domain_type::dim>(ExactSol));
  return L2Error(spExactSol, spGridFct, cmp, time, quadOrder, subsets);
}
 
template <typename TGridFunction>
number L2Error(const char* ExactSol,
               SmartPtr<TGridFunction> spGridFct, const char* cmp,
               number time, int quadOrder)
{
  return L2Error(ExactSol, spGridFct, cmp, time, quadOrder, NULL);
}
#endif
 
 
 
 
// H1 Error Integrand
 
template <typename TGridFunction>
class H1ErrorIntegrand
  : public StdIntegrand<number, TGridFunction::dim, H1ErrorIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
 
  private:
    ScalarGridFunctionData<TGridFunction> m_scalarData;
 
    SmartPtr<UserData<number, worldDim> > m_spExactSolution;
 
    SmartPtr<UserData<MathVector<worldDim>, worldDim> > m_spExactGrad;
 
    number m_time;
 
  public:
    H1ErrorIntegrand(SmartPtr<UserData<number, worldDim> > spExactSol,
                     SmartPtr<UserData<MathVector<worldDim>, worldDim> > spExactGrad,
                     TGridFunction& gridFct, size_t cmp,
                     number time)
    : m_scalarData (gridFct, cmp),
      m_spExactSolution(spExactSol),
      m_spExactGrad(spExactGrad),
      m_time(time)
    {}
 
    virtual void set_subset(int si)
    {
      if(!m_scalarData.is_def_in_subset(si))
        UG_THROW("H1Error: Grid function component"
            <<m_scalarData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID roid = pElem->reference_object_id();
 
      try{
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rTrialSpace =
              LocalFiniteElementProvider::get<elemDim>(roid, m_scalarData.id());
 
    //  number of dofs on element
      const size_t num_sh = rTrialSpace.num_sh();
 
    //  get multiindices of element
      std::vector<DoFIndex> ind;  //  aux. index array
      m_scalarData.dof_indices(pElem, ind);
 
    //  check multi indices
      if(ind.size() != num_sh)
        UG_THROW("H1ErrorIntegrand::evaluate: Wrong number of"
            " multi indices.");
 
    //  loop all integration points
      std::vector<MathVector<elemDim> > vLocGradient(num_sh);
      for(size_t ip = 0; ip < numIP; ++ip)
      {
      //  compute exact solution at integration point
        number exactSolIP;
        (*m_spExactSolution)(exactSolIP, vGlobIP[ip], m_time, this->subset());
 
      //  compute exact gradient at integration point
        MathVector<worldDim> exactGradIP;
        (*m_spExactGrad)(exactGradIP, vGlobIP[ip], m_time, this->subset());
 
      //  compute shape gradients at ip
        rTrialSpace.grads(&vLocGradient[0], vLocIP[ip]);
 
      //  compute approximated solution at integration point
        number approxSolIP = 0.0;
        MathVector<elemDim> locTmp; VecSet(locTmp, 0.0);
        for(size_t sh = 0; sh < num_sh; ++sh)
        {
        //  get value at shape point (e.g. corner for P1 fct)
          const number valSH = DoFRef(m_scalarData.grid_function(), ind[sh]);
 
        //  add shape fct at ip * value at shape
          approxSolIP += valSH * rTrialSpace.shape(sh, vLocIP[ip]);
 
        //  add gradient at ip
          VecScaleAppend(locTmp, valSH, vLocGradient[sh]);
        }
 
      //  compute global gradient
        MathVector<worldDim> approxGradIP;
        MathMatrix<worldDim, elemDim> JTInv;
        Inverse(JTInv, vJT[ip]);
        MatVecMult(approxGradIP, JTInv, locTmp);
 
      //  get squared of difference
        vValue[ip] = (exactSolIP - approxSolIP) * (exactSolIP - approxSolIP);
        vValue[ip] += VecDistanceSq(approxGradIP, exactGradIP);
      }
 
      }
      UG_CATCH_THROW("H1ErrorIntegrand::evaluate: trial space missing.");
    }
};
 
 
template <typename TGridFunction>
number H1Error(SmartPtr<UserData<number, TGridFunction::dim> > spExactSol,
               SmartPtr<UserData<MathVector<TGridFunction::dim>, TGridFunction::dim> > spExactGrad,
         SmartPtr<TGridFunction> spGridFct, const char* cmp,
         number time, int quadOrder, const char* subsets)
{
//  get function id of name
  const size_t fct = spGridFct->fct_id_by_name(cmp);
 
//  check that function exists
  if(fct >= spGridFct->num_fct())
    UG_THROW("H1Error: Function space does not contain"
        " a function with name " << cmp << ".");
 
  H1ErrorIntegrand<TGridFunction> spIntegrand(spExactSol, spExactGrad, *spGridFct, fct, time);
  return sqrt(IntegrateSubsets(spIntegrand, *spGridFct, subsets, quadOrder));
}
 
template <typename TGridFunction>
number H1Error(SmartPtr<UserData<number, TGridFunction::dim> > spExactSol,
               SmartPtr<UserData<MathVector<TGridFunction::dim>, TGridFunction::dim> > spExactGrad,
         SmartPtr<TGridFunction> spGridFct, const char* cmp,
         number time, int quadOrder)
{
  return H1Error(spExactSol, spExactGrad, spGridFct, cmp, time, quadOrder, NULL);
}
 
#ifdef UG_FOR_LUA
template <typename TGridFunction>
number H1Error(const char* ExactSol, const char* ExactGrad,
         SmartPtr<TGridFunction> spGridFct, const char* cmp,
         number time, int quadOrder, const char* subsets)
{
  static const int dim = TGridFunction::domain_type::dim;
  SmartPtr<UserData<number, dim> > spExactSol
   = make_sp(new LuaUserData<number, dim>(ExactSol));
  SmartPtr<UserData<MathVector<dim>, dim> > spExactGrad
   = make_sp(new LuaUserData<MathVector<dim>, dim>(ExactGrad));
  return H1Error(spExactSol, spExactGrad, spGridFct, cmp, time, quadOrder, subsets);
}
 
template <typename TGridFunction>
number H1Error(const char* ExactSol, const char* ExactGrad,
         SmartPtr<TGridFunction> spGridFct, const char* cmp,
         number time, int quadOrder)
{
  return H1Error(ExactSol, ExactGrad, spGridFct, cmp, time, quadOrder, NULL);
}
#endif
 
 
 
 
template <typename TDistIntegrand, typename TGridFunction>
number GridFunctionDistance2(TGridFunction& spGridFct1, const char* cmp1,
              TGridFunction& spGridFct2, const char* cmp2,
              int quadOrder, const char* subsets)
{
//  get function id of name
  const size_t fct1 = spGridFct1.fct_id_by_name(cmp1);
  const size_t fct2 = spGridFct2.fct_id_by_name(cmp2);
 
//  check that function exists
  if(fct1 >= spGridFct1.num_fct())
    UG_THROW("GridFunctionDistance: Function space does not contain"
        " a function with name " << cmp1 << ".");
  if(fct2 >= spGridFct2.num_fct())
    UG_THROW("GridFunctionDistance: Function space does not contain"
        " a function with name " << cmp2 << ".");
 
//  get top level of grid functions
  const int level1 = spGridFct1.dof_distribution()->grid_level().level();
  const int level2 = spGridFct2.dof_distribution()->grid_level().level();
 
  if(level1 > level2){
    // level check
    TDistIntegrand spIntegrand(spGridFct1, fct1, spGridFct2, fct2);
    return IntegrateSubsets(spIntegrand, spGridFct1, subsets, quadOrder);
  }else{
    TDistIntegrand spIntegrand(spGridFct2, fct2, spGridFct1, fct1);
    return IntegrateSubsets(spIntegrand, spGridFct2, subsets, quadOrder);
  }
 
}
 
template <typename TDistIntegrand, typename TGridFunction>
number GridFunctionDistance2(TGridFunction& spGridFct1, const char* cmp1,
               TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets, ConstSmartPtr<typename TDistIntegrand::weight_type> spWeights)
{
//  get function id of name
  const size_t fct1 = spGridFct1.fct_id_by_name(cmp1);
  const size_t fct2 = spGridFct2.fct_id_by_name(cmp2);
 
//  check that function exists
  if(fct1 >= spGridFct1.num_fct())
    UG_THROW("GridFunctionDistance: Function space does not contain"
        " a function with name " << cmp1 << ".");
  if(fct2 >= spGridFct2.num_fct())
    UG_THROW("GridFunctionDistance: Function space does not contain"
        " a function with name " << cmp2 << ".");
 
//  get top level of gridfunctions
  const int level1 = spGridFct1.dof_distribution()->grid_level().level();
  const int level2 = spGridFct2.dof_distribution()->grid_level().level();
 
  // w/ weights
  if(level1 > level2){
    TDistIntegrand spIntegrand(spGridFct1, fct1, spGridFct2, fct2, spWeights);
    return IntegrateSubsets(spIntegrand, spGridFct1, subsets, quadOrder);
  }else{
    TDistIntegrand spIntegrand(spGridFct2, fct2, spGridFct1, fct1, spWeights);
    return IntegrateSubsets(spIntegrand, spGridFct2, subsets, quadOrder);
  }
}
 
 
template <typename TDistIntegrand, typename TGridFunction>
number GridFunctionDistance2(TGridFunction& spGridFct1, const char* cmp1,
               TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets,
         ConstSmartPtr<typename TDistIntegrand::weight_type> spWeights,
         number distAvg12)
{
//  get function id of name
  const size_t fct1 = spGridFct1.fct_id_by_name(cmp1);
  const size_t fct2 = spGridFct2.fct_id_by_name(cmp2);
 
//  check that function exists
  if(fct1 >= spGridFct1.num_fct())
    UG_THROW("GridFunctionDistance: Function space does not contain"
        " a function with name " << cmp1 << ".");
  if(fct2 >= spGridFct2.num_fct())
    UG_THROW("GridFunctionDistance: Function space does not contain"
        " a function with name " << cmp2 << ".");
 
//  get top level of gridfunctions
  const int level1 = spGridFct1.dof_distribution()->grid_level().level();
  const int level2 = spGridFct2.dof_distribution()->grid_level().level();
 
  // w/ weights
  if(level1 > level2){
    TDistIntegrand spIntegrand(spGridFct1, fct1, spGridFct2, fct2, spWeights, distAvg12);
    return IntegrateSubsets(spIntegrand, spGridFct1, subsets, quadOrder);
  }else{
    TDistIntegrand spIntegrand(spGridFct2, fct2, spGridFct1, fct1, spWeights, -distAvg12);
    return IntegrateSubsets(spIntegrand, spGridFct2, subsets, quadOrder);
  }
}
 
 
 
// L2 Integrand
 
template <typename TGridFunction>
class L2Integrand
  : public StdIntegrand<number, TGridFunction::dim, L2Integrand<TGridFunction> >
{
  public:
  //  world dimension of grid function
    static const int worldDim = TGridFunction::dim;
    typedef UserData<number, worldDim> weight_type;
 
  protected:
  // grid function data
    ScalarGridFunctionData<TGridFunction> m_scalarData;
 
    ConstSmartPtr<weight_type> m_spWeight;
 
  public:
    L2Integrand(TGridFunction& spGridFct, size_t cmp)
    : m_scalarData(spGridFct, cmp), m_spWeight(make_sp(new ConstUserNumber<worldDim>(1.0)))
    {};
 
    L2Integrand(TGridFunction& spGridFct, size_t cmp, ConstSmartPtr<weight_type> spWeight)
    : m_scalarData(spGridFct, cmp), m_spWeight(spWeight)
    {};
 
    virtual ~L2Integrand() {};
 
    virtual void set_subset(int si)
    {
      if(!m_scalarData.is_def_in_subset(si))
        UG_THROW("L2ErrorIntegrand: Grid function component" <<m_scalarData.fct() <<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      ReferenceObjectID roid = (ReferenceObjectID) pElem->reference_object_id();
 
    // element weights
      typedef typename weight_type::data_type ipdata_type;
      std::vector<ipdata_type> locElemWeights(numIP, 1.0);
      UG_ASSERT(m_spWeight.valid(), "L2Integrand::evaluate requires valid weights!");
      (*m_spWeight)(&locElemWeights[0], vGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), numIP);
 
      try{
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rTrialSpace =
              LocalFiniteElementProvider::get<elemDim>(roid, m_scalarData.id());
 
    //  number of dofs on element
      const size_t num_sh = rTrialSpace.num_sh();
 
    //  get multiindices of element
      std::vector<DoFIndex> ind;  //  aux. index array
      m_scalarData.dof_indices(pElem, ind);
 
    //  check multi indices
      if(ind.size() != num_sh)
        UG_THROW("L2Integrand::evaluate: Wrong number of multi indices.");
 
    //  loop all integration points
      for(size_t ip = 0; ip < numIP; ++ip)
      {
 
      //  compute approximated solution at integration point
        number approxSolIP = 0.0;
        for(size_t sh = 0; sh < num_sh; ++sh)
        {
          //  get value at shape point (e.g. corner for P1 fct)
          //  and add shape fct at ip * value at shape
          const number valSH = DoFRef(m_scalarData.grid_function(), ind[sh]);
          approxSolIP += valSH * rTrialSpace.shape(sh, vLocIP[ip]);
        }
 
        //  get square
        vValue[ip] = locElemWeights[ip]*approxSolIP*approxSolIP;
 
      }
 
      }
      UG_CATCH_THROW("L2FuncIntegrand::values: trial space missing.");
    }
};
 
template <typename TGridFunction>
number L2Norm2(TGridFunction& u, const char* cmp,
              int quadOrder, const char* subsets,
        ConstSmartPtr<typename L2Integrand<TGridFunction>::weight_type> spWeight)
{
//  get function id of name
  const size_t fct = u.fct_id_by_name(cmp);
 
//  check that function exists
  UG_COND_THROW(fct >= u.num_fct(), "L2Norm: Function space does not contain"
        " a function with name " << cmp << ".");
 
  L2Integrand<TGridFunction> integrandL2(u, fct, spWeight);
  return IntegrateSubsets(integrandL2, u, subsets, quadOrder);
}
 
template <typename TGridFunction>
number L2Norm2(TGridFunction& u, const char* cmp,
              int quadOrder, const char* subsets)
{
//  get function id of name
  const size_t fct = u.fct_id_by_name(cmp);
 
//  check that function exists
  UG_COND_THROW(fct >= u.num_fct(), "L2Norm: Function space does not contain"
        " a function with name " << cmp << ".");
 
  L2Integrand<TGridFunction> integrandL2(u, fct);
  return IntegrateSubsets(integrandL2, u, subsets, quadOrder);
}
 
template <typename TGridFunction>
number L2Norm(TGridFunction& u, const char* cmp,
              int quadOrder, const char* subsets)
{
  return sqrt(L2Norm2(u, cmp, quadOrder, subsets));
}
template <typename TGridFunction>
number L2Norm(TGridFunction& gridFct, const char* cmp, int quadOrder)
{ return L2Norm(gridFct, cmp, quadOrder, NULL); }
 
template <typename TGridFunction>
number L2Norm(SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder, const char* subsets)
{ return L2Norm(*spGridFct, cmp, quadOrder, subsets); }
 
template <typename TGridFunction>
number L2Norm(SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder)
{ return L2Norm(spGridFct, cmp, quadOrder, NULL); }
 
 
template <typename TGridFunction>
class L2DistIntegrand
    : public StdIntegrand<number, TGridFunction::dim, L2DistIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
    typedef typename L2Integrand<TGridFunction>::weight_type weight_type;
 
  protected:
    ScalarGridFunctionData<TGridFunction> m_fineData;
    const int m_fineTopLevel;
 
    ScalarGridFunctionData<TGridFunction> m_coarseData;
    const int m_coarseTopLevel;
 
    SmartPtr<MultiGrid> m_spMG;
 
    ConstSmartPtr<weight_type> m_spWeight;
 
    double m_deltaFineCoarse;
 
  public:
 
    L2DistIntegrand(TGridFunction& fineGridFct, size_t fineCmp,
          TGridFunction& coarseGridFct, size_t coarseCmp)
    : m_fineData(fineGridFct, fineCmp), m_fineTopLevel(fineGridFct.dof_distribution()->grid_level().level()),
      m_coarseData(coarseGridFct, coarseCmp), m_coarseTopLevel(coarseGridFct.dof_distribution()->grid_level().level()),
      m_spMG(m_fineData.domain()->grid()), m_spWeight(make_sp(new ConstUserNumber<TGridFunction::dim>(1.0))),
      m_deltaFineCoarse(0.0)
    {
      UG_COND_THROW(m_fineTopLevel < m_coarseTopLevel,
        "L2DiffIntegrand: fine and top level inverted.");
      UG_COND_THROW(m_fineData.domain().get() != m_coarseData.domain().get(),
        "L2DiffIntegrand: grid functions defined on different domains.");
    };
 
    L2DistIntegrand(TGridFunction& fineGridFct, size_t fineCmp,
          TGridFunction& coarseGridFct, size_t coarseCmp, ConstSmartPtr<weight_type> spWeight)
    : m_fineData(fineGridFct, fineCmp), m_fineTopLevel(fineGridFct.dof_distribution()->grid_level().level()),
      m_coarseData(coarseGridFct, coarseCmp), m_coarseTopLevel(coarseGridFct.dof_distribution()->grid_level().level()),
      m_spMG(m_fineData.domain()->grid()), m_spWeight(spWeight),
      m_deltaFineCoarse(0.0)
    {
      UG_COND_THROW(m_fineTopLevel < m_coarseTopLevel,
          "L2DiffIntegrand: fine and top level inverted.");
      UG_COND_THROW(m_fineData.domain().get() != m_coarseData.domain().get(),
          "L2DiffIntegrand: grid functions defined on different domains.");
    };
 
    L2DistIntegrand(TGridFunction& fineGridFct, size_t fineCmp,
        TGridFunction& coarseGridFct, size_t coarseCmp, ConstSmartPtr<weight_type> spWeight, number dist12)
    : m_fineData(fineGridFct, fineCmp), m_fineTopLevel(fineGridFct.dof_distribution()->grid_level().level()),
      m_coarseData(coarseGridFct, coarseCmp), m_coarseTopLevel(coarseGridFct.dof_distribution()->grid_level().level()),
      m_spMG(m_fineData.domain()->grid()), m_spWeight(spWeight),
      m_deltaFineCoarse(dist12)
    {
      UG_COND_THROW(m_fineTopLevel < m_coarseTopLevel,
          "L2DiffIntegrand: fine and top level inverted.");
      UG_COND_THROW(m_fineData.domain().get() != m_coarseData.domain().get(),
          "L2DiffIntegrand: grid functions defined on different domains.");
    };
 
 
    virtual ~L2DistIntegrand() {}
 
    virtual void set_subset(int si)
    {
      UG_COND_THROW(!m_fineData.is_def_in_subset(si),
        "L2DiffIntegrand: Grid function component" <<m_fineData.fct()<<" not defined on subset "<<si);
      UG_COND_THROW(!m_coarseData.is_def_in_subset(si),
        "L2DiffIntegrand: Grid function component" <<m_coarseData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vFineGlobIP[],
                  GridObject* pFineElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vFineLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
      typedef typename TGridFunction::template dim_traits<elemDim>::grid_base_object Element;
 
      //  get coarse element
      GridObject* pCoarseElem = pFineElem;
      if(m_coarseTopLevel < m_fineTopLevel){
        int parentLevel = m_spMG->get_level(pCoarseElem);
        while(parentLevel > m_coarseTopLevel){
          pCoarseElem = m_spMG->get_parent(pCoarseElem);
          parentLevel = m_spMG->get_level(pCoarseElem);
        }
      }
 
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID fineROID = pFineElem->reference_object_id();
      const ReferenceObjectID coarseROID = pCoarseElem->reference_object_id();
 
    //  get corner coordinates
      std::vector<MathVector<worldDim> > vCornerCoarse;
      CollectCornerCoordinates(vCornerCoarse, *static_cast<Element*>(pCoarseElem), *m_coarseData.domain());
 
    //  get Reference Mapping
      DimReferenceMapping<elemDim, worldDim>& map
        = ReferenceMappingProvider::get<elemDim, worldDim>(coarseROID, vCornerCoarse);
 
      std::vector<MathVector<elemDim> > vCoarseLocIP;
      vCoarseLocIP.resize(numIP);
      for(size_t ip = 0; ip < vCoarseLocIP.size(); ++ip) VecSet(vCoarseLocIP[ip], 0.0);
      map.global_to_local(&vCoarseLocIP[0], vFineGlobIP, numIP);
 
    // element weights
      typedef typename weight_type::data_type ipdata_type;
      std::vector<ipdata_type> fineElemWeights(numIP, 1.0);
      UG_ASSERT(m_spWeight.valid(), "L2DistIntegrand::evaluate requires valid weights! ");
      (*m_spWeight)(&fineElemWeights[0], vFineGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), numIP);
 
    try{
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rFineLSFS =
          LocalFiniteElementProvider::get<elemDim>(fineROID, m_fineData.id());
      const LocalShapeFunctionSet<elemDim>& rCoarseLSFS =
          LocalFiniteElementProvider::get<elemDim>(coarseROID, m_coarseData.id());
 
    //  get multiindices of element
      std::vector<DoFIndex> vFineMI, vCoarseMI;
      m_fineData.dof_indices(pFineElem, vFineMI);
      m_coarseData.dof_indices(pCoarseElem, vCoarseMI);
 
    //  loop all integration points
      for(size_t ip = 0; ip < numIP; ++ip)
      {
      //  compute approximated solution at integration point
        number fineSolIP = 0.0;
        for(size_t sh = 0; sh < vFineMI.size(); ++sh)
        {
        //  get value at shape point (e.g. corner for P1 fct)
          const number val = DoFRef(m_fineData.grid_function(), vFineMI[sh]);
 
        //  add shape fct at ip * value at shape
          fineSolIP += val * rFineLSFS.shape(sh, vFineLocIP[ip]);
        }
        number coarseSolIP = 0.0;
        for(size_t sh = 0; sh < vCoarseMI.size(); ++sh)
        {
        //  get value at shape point (e.g. corner for P1 fct)
          const number val = DoFRef(m_coarseData.grid_function(), vCoarseMI[sh]);
 
        //  add shape fct at ip * value at shape
          coarseSolIP += val * rCoarseLSFS.shape(sh, vCoarseLocIP[ip]);
        }
 
      //  get squared of difference
        vValue[ip] = fineElemWeights[ip]*(fineSolIP - coarseSolIP -m_deltaFineCoarse)*(fineSolIP-coarseSolIP-m_deltaFineCoarse);
      }
 
      }
      UG_CATCH_THROW("L2DistIntegrand::evaluate: trial space missing.");
    }
};
 
 
template <typename TGridFunction>
number L2Distance2(TGridFunction& spGridFct1, const char* cmp1,
               TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets,
         ConstSmartPtr<typename L2Integrand<TGridFunction>::weight_type> spWeight, number avgDist12=0.0)
{
  return GridFunctionDistance2<L2DistIntegrand<TGridFunction>, TGridFunction>
    (spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, subsets, spWeight, avgDist12);
}
 
 
template <typename TGridFunction>
number L2Distance2(TGridFunction& spGridFct1, const char* cmp1,
               TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets)
{
  return GridFunctionDistance2<L2DistIntegrand<TGridFunction>, TGridFunction>
    (spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, subsets);
}
 
template <typename TGridFunction>
number L2Distance(TGridFunction& spGridFct1, const char* cmp1,
               TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets)
{
  return sqrt(L2Distance2(spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, subsets));
}
 
 
template <typename TGridFunction>
number L2Error(SmartPtr<TGridFunction> spGridFct1, const char* cmp1,
               SmartPtr<TGridFunction> spGridFct2, const char* cmp2,
               int quadOrder)
{
  return L2Distance(*spGridFct1, cmp1, *spGridFct2, cmp2, quadOrder, NULL);
}
 
template <typename TGridFunction>
number L2Error(SmartPtr<TGridFunction> spGridFct1, const char* cmp1,
               SmartPtr<TGridFunction> spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets)
{
  return L2Distance(*spGridFct1, cmp1, *spGridFct2, cmp2, quadOrder, subsets);
}
 
// H1 semi-norm Integrand
 
 
 
template <typename TGridFunction>
class H1SemiIntegrand
  : public StdIntegrand<number, TGridFunction::dim, H1SemiIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
    typedef UserData<MathMatrix<worldDim, worldDim>, worldDim> weight_type;
 
  protected:
    ScalarGridFunctionData<TGridFunction> m_scalarData;
 
    ConstSmartPtr<weight_type> m_spWeight;
 
  public:
    H1SemiIntegrand(TGridFunction& gridFct, size_t cmp)
    : m_scalarData(gridFct, cmp), m_spWeight(make_sp(new ConstUserMatrix<worldDim>(1.0))) {}
 
    H1SemiIntegrand(TGridFunction& gridFct, size_t cmp, ConstSmartPtr<weight_type> spWeight)
    : m_scalarData(gridFct, cmp), m_spWeight(spWeight) {}
 
    virtual ~H1SemiIntegrand() {};
 
    virtual void set_subset(int si)
    {
 
      UG_COND_THROW(!m_scalarData.is_def_in_subset(si), "H1Error: Grid function component"
            <<m_scalarData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID roid = pElem->reference_object_id();
      const TGridFunction &gridFct= m_scalarData.grid_function();
 
      typedef typename weight_type::data_type ipdata_type;
 
      std::vector<ipdata_type> elemWeights(numIP, MathMatrix<worldDim, worldDim>());
      UG_ASSERT(m_spWeight.valid(), "H1SemiIntegrand::evaluate requires valid weights!");
 
 
      if(m_spWeight->requires_grid_fct())
      {
        //  get local solution if needed
        LocalIndices ind;
        LocalVector uloc;
        gridFct.indices(pElem, ind);  //  get global indices
        uloc.resize(ind);       //  adapt local algebra
        GetLocalVector(uloc, gridFct);  //  read local values of u
 
        //  compute data
        try{
          (*m_spWeight)(&elemWeights[0], vGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), pElem,
              vCornerCoords, vLocIP, numIP, &uloc, NULL);
        } UG_CATCH_THROW("H1SemiIntegrand: Cannot evaluate weight data.");
      }
      else
      {
        //  compute data
        try{
          (*m_spWeight)(&elemWeights[0], vGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), numIP);
        } UG_CATCH_THROW("H1SemiIntegrand: Cannot evaluate weight data.");
      }
 
 
      try{
 
 
 
 
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rTrialSpace =
              LocalFiniteElementProvider::get<elemDim>(roid, m_scalarData.id());
 
    //  number of dofs on element
      const size_t num_sh = rTrialSpace.num_sh();
 
    //  get multiindices of element
      std::vector<DoFIndex> ind;  //  aux. index array
      gridFct.dof_indices(pElem, m_scalarData.fct(), ind);
 
    //  check multi indices
      UG_COND_THROW(ind.size() != num_sh, "H1SemiNormFuncIntegrand::evaluate: Wrong number of multi-)indices.");
 
    //  loop all integration points
      std::vector<MathVector<elemDim> > vLocGradient(num_sh);
      for(size_t ip = 0; ip < numIP; ++ip)
      {
      //  compute shape gradients at ip
        rTrialSpace.grads(&vLocGradient[0], vLocIP[ip]);
 
      //  compute approximated solution at integration point
        number approxSolIP = 0.0;
        MathVector<elemDim> tmpVec(0.0);
        for(size_t sh = 0; sh < num_sh; ++sh)
        {
        //  get value at shape point (e.g. corner for P1 fct)
          const number valSH = DoFRef(gridFct, ind[sh]);
 
        //  add shape fct at ip * value at shape
          approxSolIP += valSH * rTrialSpace.shape(sh, vLocIP[ip]);
 
        //  add gradient at ip
          VecScaleAppend(tmpVec, valSH, vLocGradient[sh]);
        }
 
      //  compute gradient
        MathVector<worldDim> approxGradIP;
        MathMatrix<worldDim, elemDim> JTInv;
        Inverse(JTInv, vJT[ip]);
        MatVecMult(approxGradIP, JTInv, tmpVec);
 
      //  get norm squared
        MathVector<worldDim> approxDGradIP;
        MatVecMult(approxDGradIP, elemWeights[ip], approxGradIP);
        vValue[ip] = VecDot(approxDGradIP, approxGradIP);
      }
 
      }
      UG_CATCH_THROW("H1SemiIntegrand::evaluate: trial space missing.");
    }
};
 
 
 
template <typename TGridFunction>
number H1SemiNorm2(TGridFunction& gridFct, const char* cmp, int quadOrder, const char* subsets=NULL,
        ConstSmartPtr<typename H1SemiIntegrand<TGridFunction>::weight_type> weights = SPNULL)
{
//  get function id of name
  const size_t fct = gridFct.fct_id_by_name(cmp);
 
//  check that function exists
  UG_COND_THROW(fct >= gridFct.num_fct(), "H1SemiNorm: Function space does not contain"
        " a function with name " << cmp << ".");
  if  (weights.invalid()) {
    H1SemiIntegrand<TGridFunction> integrand(gridFct, fct);
    return IntegrateSubsets(integrand, gridFct, subsets, quadOrder);
  } else {
    H1SemiIntegrand<TGridFunction> integrand(gridFct, fct, weights);
    return IntegrateSubsets(integrand, gridFct, subsets, quadOrder);
  }
}
 
template <typename TGridFunction>
number H1SemiNorm(TGridFunction& gridFct, const char* cmp, int quadOrder, const char* subsets=NULL,
        ConstSmartPtr<typename H1SemiIntegrand<TGridFunction>::weight_type> weights = SPNULL)
{
  return (sqrt(H1SemiNorm2(gridFct, cmp, quadOrder, subsets, weights)));
}
 
// Delegating to H1SemiNorm
template <typename TGridFunction>
number H1SemiNorm(SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder, const char* subsets)
{ return H1SemiNorm(*spGridFct, cmp, quadOrder, subsets); }
 
template <typename TGridFunction>
number H1SemiNorm(SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder,
    const char* subsets, ConstSmartPtr<typename H1SemiIntegrand<TGridFunction>::weight_type> weights = SPNULL)
{ return H1SemiNorm(*spGridFct, cmp, quadOrder, subsets, weights); }
 
template <typename TGridFunction>
number H1SemiNorm( SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder)
{ return H1SemiNorm(*spGridFct, cmp, quadOrder, NULL); }
 
template <typename TGridFunction>
number H1SemiNorm( SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder,
    ConstSmartPtr<typename H1SemiIntegrand<TGridFunction>::weight_type> weights)
{ return H1SemiNorm(*spGridFct, cmp, quadOrder, NULL, weights); }
 
template <typename TGridFunction>
class H1SemiDistIntegrand : public StdIntegrand<number, TGridFunction::dim, H1SemiDistIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
    typedef typename H1SemiIntegrand<TGridFunction>::weight_type weight_type;
 
  private:
    ScalarGridFunctionData<TGridFunction> m_fineData;
    const int m_fineTopLevel;
 
    ScalarGridFunctionData<TGridFunction> m_coarseData;
    const int m_coarseTopLevel;
 
    SmartPtr<MultiGrid> m_spMG;
 
    ConstSmartPtr<weight_type> m_spWeight;
 
  public:
    H1SemiDistIntegrand(TGridFunction& fineGridFct, size_t fineCmp,
              TGridFunction& coarseGridFct, size_t coarseCmp)
    : m_fineData(fineGridFct, fineCmp),
      m_fineTopLevel(fineGridFct.dof_distribution()->grid_level().level()),
      m_coarseData(coarseGridFct, coarseCmp),
      m_coarseTopLevel(coarseGridFct.dof_distribution()->grid_level().level()),
      m_spMG(fineGridFct.domain()->grid()),
      m_spWeight(new ConstUserNumber<TGridFunction::dim>(1.0))
    {
      if(m_fineTopLevel < m_coarseTopLevel)
        UG_THROW("H1SemiDiffIntegrand: fine and top level inverted.");
 
      if(m_fineData.domain().get() != m_coarseData.domain().get())
        UG_THROW("H1SemiDiffIntegrand: grid functions defined on different domains.");
    };
 
    H1SemiDistIntegrand(TGridFunction& fineGridFct, size_t fineCmp,
              TGridFunction& coarseGridFct, size_t coarseCmp,
              ConstSmartPtr<weight_type> spWeight)
    : m_fineData(fineGridFct, fineCmp),
      m_fineTopLevel(fineGridFct.dof_distribution()->grid_level().level()),
      m_coarseData(coarseGridFct, coarseCmp),
      m_coarseTopLevel(coarseGridFct.dof_distribution()->grid_level().level()),
      m_spMG(fineGridFct.domain()->grid()),
      m_spWeight(spWeight)
    {
      UG_COND_THROW(m_fineTopLevel < m_coarseTopLevel, "H1SemiDiffIntegrand: fine and top level inverted.");
      UG_COND_THROW(m_fineData.domain().get() != m_coarseData.domain().get(), "H1SemiDiffIntegrand: grid functions defined on different domains.");
    }
    virtual ~H1SemiDistIntegrand(){}
 
    virtual void set_subset(int si)
    {
 
      UG_COND_THROW(!m_fineData.is_def_in_subset(si), "H1SemiDiffIntegrand: Grid function component"
             <<m_fineData.fct()<<" not defined on subset "<<si);
      UG_COND_THROW(!m_coarseData.is_def_in_subset(si), "H1SemiDiffIntegrand: Grid function component"
            <<m_coarseData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vFineGlobIP[],
                  GridObject* pFineElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vFineLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
      typedef typename TGridFunction::template dim_traits<elemDim>::grid_base_object Element;
 
      const TGridFunction &fineGridFct  = m_fineData.grid_function();
      const TGridFunction &coarseGridFct  = m_coarseData.grid_function();
 
      //  get coarse element
      GridObject* pCoarseElem = pFineElem;
      if(m_coarseTopLevel < m_fineTopLevel){
        int parentLevel = m_spMG->get_level(pCoarseElem);
        while(parentLevel > m_coarseTopLevel){
          pCoarseElem = m_spMG->get_parent(pCoarseElem);
          parentLevel = m_spMG->get_level(pCoarseElem);
        }
      }
 
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID fineROID = pFineElem->reference_object_id();
      const ReferenceObjectID coarseROID = pCoarseElem->reference_object_id();
 
    //  get corner coordinates
      std::vector<MathVector<worldDim> > vCornerCoarse;
      CollectCornerCoordinates(vCornerCoarse, *static_cast<Element*>(pCoarseElem), *m_coarseData.domain());
 
    //  get reference Mapping
      DimReferenceMapping<elemDim, worldDim>& map
        = ReferenceMappingProvider::get<elemDim, worldDim>(coarseROID, vCornerCoarse);
 
      std::vector<MathVector<elemDim> > vCoarseLocIP;
      vCoarseLocIP.resize(numIP);
      for(size_t ip = 0; ip < vCoarseLocIP.size(); ++ip) VecSet(vCoarseLocIP[ip], 0.0);
      map.global_to_local(&vCoarseLocIP[0], vFineGlobIP, numIP);
 
 
      // determine weights
      std::vector<typename weight_type::data_type> elemWeights(numIP, MathMatrix<worldDim, worldDim>());
      UG_ASSERT(m_spWeight.valid(), "H1SemiDistIntegrand::evaluate requires valid weights!");
 
      //  get local solution (if required)
      if(m_spWeight->requires_grid_fct())
      {
 
        LocalIndices ind;
        LocalVector u;
        fineGridFct.indices(pFineElem, ind);  //  get global indices
        u.resize(ind);              //  adapt local algebra
        GetLocalVector(u, fineGridFct);     //  read local values of u
 
        //  compute data
        try{
          (*m_spWeight)(&elemWeights[0], vFineGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), pFineElem,
              vCornerCoords, vFineLocIP, numIP, &u, NULL);
        } UG_CATCH_THROW("H1SemiDistIntegrand: Cannot evaluate data.");
      }
      else
      {
        //  compute data
        try{
          (*m_spWeight)(&elemWeights[0], vFineGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), numIP);
        } UG_CATCH_THROW("H1SemiDistIntegrand: Cannot evaluate data.");
      }
 
      try{
 
 
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rFineLSFS =
          LocalFiniteElementProvider::get<elemDim>(fineROID, m_fineData.id());
      const LocalShapeFunctionSet<elemDim>& rCoarseLSFS =
          LocalFiniteElementProvider::get<elemDim>(coarseROID, m_coarseData.id());
 
    //  get multiindices of element
      std::vector<DoFIndex> vFineMI, vCoarseMI;
      m_fineData.dof_indices(pFineElem, vFineMI);
      m_coarseData.dof_indices(pCoarseElem, vCoarseMI);
 
      std::vector<MathVector<elemDim> > vFineLocGradient(vFineMI.size());
      std::vector<MathVector<elemDim> > vCoarseLocGradient(vCoarseMI.size());
 
    //  loop all integration points
      for(size_t ip = 0; ip < numIP; ++ip)
      {
      //  compute shape gradients at ip
        rFineLSFS.grads(&vFineLocGradient[0], vFineLocIP[ip]);
        rCoarseLSFS.grads(&vCoarseLocGradient[0], vCoarseLocIP[ip]);
 
      //  compute approximated solutions at integration point
        number fineSolIP = 0.0;
        MathVector<elemDim> fineLocTmp(0.0);
        for(size_t sh = 0; sh < vFineMI.size(); ++sh)
        {
          const number val = DoFRef(fineGridFct, vFineMI[sh]);
          fineSolIP += val * rFineLSFS.shape(sh, vFineLocIP[ip]);
          VecScaleAppend(fineLocTmp, val, vFineLocGradient[sh]);
        }
 
        number coarseSolIP = 0.0;
        MathVector<elemDim> coarseLocTmp(0.0);
        for(size_t sh = 0; sh < vCoarseMI.size(); ++sh)
        {
          const number val = DoFRef(coarseGridFct, vCoarseMI[sh]);
          coarseSolIP += val * rCoarseLSFS.shape(sh, vCoarseLocIP[ip]);
          VecScaleAppend(coarseLocTmp, val, vCoarseLocGradient[sh]);
        }
 
      //  compute global gradient
        MathVector<worldDim> fineGradIP;
        MathMatrix<worldDim, elemDim> fineJTInv;
        Inverse(fineJTInv, vJT[ip]);
        MatVecMult(fineGradIP, fineJTInv, fineLocTmp);
 
      //  compute global gradient
        MathVector<worldDim> coarseGradIP;
        MathMatrix<worldDim, elemDim> coarseJTInv;
        map.jacobian_transposed_inverse(coarseJTInv, vCoarseLocIP[ip]);
        MatVecMult(coarseGradIP, coarseJTInv, coarseLocTmp);
 
      //  get squared of difference
        /*vValue[ip] = (coarseSolIP - fineSolIP);
        vValue[ip] *= vValue[ip]; */
        vValue[ip] = VecDistanceSq(coarseGradIP, fineGradIP, elemWeights[ip]);
      }
 
      }
      UG_CATCH_THROW("H1SemiDiffIntegrand::evaluate: trial space missing.");
    }
};
 
 
template <typename TGridFunction>
number H1SemiError2(SmartPtr<TGridFunction> spGridFct1, const char* cmp1,
               SmartPtr<TGridFunction> spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets)
{
  return GridFunctionDistance2<H1SemiDistIntegrand<TGridFunction>, TGridFunction>
    (*spGridFct1, cmp1, *spGridFct2, cmp2, quadOrder, subsets);
}
 
template <typename TGridFunction>
number H1SemiError(SmartPtr<TGridFunction> spGridFct1, const char* cmp1,
               SmartPtr<TGridFunction> spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets)
{
  return sqrt(H1SemiError2(*spGridFct1, cmp1, *spGridFct2, cmp2, quadOrder, subsets));
}
 
template <typename TGridFunction>
number H1SemiError(SmartPtr<TGridFunction> spGridFct1, const char* cmp1,
               SmartPtr<TGridFunction> spGridFct2, const char* cmp2,
               int quadOrder)
{
  return H1SemiError(*spGridFct1, cmp1, *spGridFct2, cmp2, quadOrder, NULL);
}
 
template <typename TGridFunction>
number H1SemiDistance2(TGridFunction& spGridFct1, const char* cmp1,
    TGridFunction& spGridFct2, const char* cmp2,
        int quadOrder, const char* subsets,
    ConstSmartPtr<typename H1SemiDistIntegrand<TGridFunction>::weight_type> weights)
{
  return GridFunctionDistance2<H1SemiDistIntegrand<TGridFunction>, TGridFunction>
    (spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, subsets, weights);
}
 
template <typename TGridFunction>
number H1SemiDistance(TGridFunction& spGridFct1, const char* cmp1,
    TGridFunction& spGridFct2, const char* cmp2,
        int quadOrder, const char* subsets,
    ConstSmartPtr<typename H1SemiDistIntegrand<TGridFunction>::weight_type> weights)
{ return sqrt(H1SemiDistance2(spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, subsets, weights)); }
 
template <typename TGridFunction>
number H1SemiDistance2(TGridFunction& spGridFct1, const char* cmp1,
            TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, ConstSmartPtr<typename H1SemiDistIntegrand<TGridFunction>::weight_type > weights)
{ return H1SemiDistance2(spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, NULL, weights); }
 
template <typename TGridFunction>
number H1SemiDistance(TGridFunction& spGridFct1, const char* cmp1,
            TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, ConstSmartPtr<typename H1SemiDistIntegrand<TGridFunction>::weight_type > weights)
{ return sqrt(H1SemiDistance2(spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, NULL, weights)); }
 
 
 
 
// H1 semi-norm Integrand
 
template <typename TGridFunction>
class H1EnergyIntegrand
  : public StdIntegrand<number, TGridFunction::dim, H1EnergyIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
    typedef UserData<MathMatrix<worldDim, worldDim>, worldDim> weight_type;
 
  protected:
    ScalarGridFunctionData<TGridFunction> m_scalarData;
 
    ConstSmartPtr<weight_type> m_spWeight;
 
  public:
    H1EnergyIntegrand(TGridFunction& gridFct, size_t cmp)
    : m_scalarData(gridFct, cmp), m_spWeight(make_sp(new ConstUserMatrix<worldDim>(1.0))) {}
 
    H1EnergyIntegrand(TGridFunction& gridFct, size_t cmp, ConstSmartPtr<weight_type> spWeight)
    : m_scalarData(gridFct, cmp), m_spWeight(spWeight) {}
 
    virtual ~H1EnergyIntegrand() {};
 
    virtual void set_subset(int si)
    {
 
      UG_COND_THROW(!m_scalarData.is_def_in_subset(si), "H1EnergyIntegrand: Grid function component"
            <<m_scalarData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID roid = pElem->reference_object_id();
      const TGridFunction &gridFct= m_scalarData.grid_function();
 
      typedef typename weight_type::data_type ipdata_type;
 
      std::vector<ipdata_type> elemWeights(numIP, MathMatrix<worldDim, worldDim>());
      UG_ASSERT(m_spWeight.valid(), "H1EnergyIntegrand::evaluate requires valid weights!");
 
 
      if(m_spWeight->requires_grid_fct())
      {
        //  get local solution if needed
        LocalIndices ind;
        LocalVector uloc;
        gridFct.indices(pElem, ind);  //  get global indices
        uloc.resize(ind);       //  adapt local algebra
        GetLocalVector(uloc, gridFct);  //  read local values of u
 
        //  compute data
        try{
          (*m_spWeight)(&elemWeights[0], vGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), pElem,
              vCornerCoords, vLocIP, numIP, &uloc, NULL);
        } UG_CATCH_THROW("H1EnergyIntegrand: Cannot evaluate weight data.");
      }
      else
      {
        //  compute data
        try{
          (*m_spWeight)(&elemWeights[0], vGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), numIP);
        } UG_CATCH_THROW("H1EnergyIntegrand: Cannot evaluate weight data.");
      }
 
 
      try{
 
 
 
 
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rTrialSpace =
              LocalFiniteElementProvider::get<elemDim>(roid, m_scalarData.id());
 
    //  number of dofs on element
      const size_t num_sh = rTrialSpace.num_sh();
 
    //  get multiindices of element
      std::vector<DoFIndex> ind;  //  aux. index array
      gridFct.dof_indices(pElem, m_scalarData.fct(), ind);
 
    //  check multi indices
      UG_COND_THROW(ind.size() != num_sh, "H1EnergyIntegrand::evaluate: Wrong number of multi-)indices.");
 
    //  loop all integration points
      std::vector<MathVector<elemDim> > vLocGradient(num_sh);
      for(size_t ip = 0; ip < numIP; ++ip)
      {
      //  compute shape gradients at ip
        rTrialSpace.grads(&vLocGradient[0], vLocIP[ip]);
 
      //  compute approximated solution at integration point
        number approxSolIP = 0.0;
        MathVector<elemDim> tmpVec(0.0);
        for(size_t sh = 0; sh < num_sh; ++sh)
        {
        //  get value at shape point (e.g. corner for P1 fct)
          const number valSH = DoFRef(gridFct, ind[sh]);
 
        //  add shape fct at ip * value at shape
          approxSolIP += valSH * rTrialSpace.shape(sh, vLocIP[ip]);
 
        //  add gradient at ip
          VecScaleAppend(tmpVec, valSH, vLocGradient[sh]);
        }
 
      //  compute gradient
        MathVector<worldDim> approxGradIP;
        MathMatrix<worldDim, elemDim> JTInv;
        Inverse(JTInv, vJT[ip]);
        MatVecMult(approxGradIP, JTInv, tmpVec);
 
      //  get norm squared
        MathVector<worldDim> approxDGradIP;
        MatVecMult(approxDGradIP, elemWeights[ip], approxGradIP);
        vValue[ip] = VecTwoNormSq(approxDGradIP);
      }
 
      }
      UG_CATCH_THROW("H1EnergyIntegrand::evaluate: trial space missing.");
    }
};
 
 
 
template <typename TGridFunction>
number H1EnergyNorm2(TGridFunction& gridFct, const char* cmp, int quadOrder, const char* subsets=NULL,
        ConstSmartPtr<typename H1SemiIntegrand<TGridFunction>::weight_type> weights = SPNULL)
{
//  get function id of name
  const size_t fct = gridFct.fct_id_by_name(cmp);
 
//  check that function exists
  UG_COND_THROW(fct >= gridFct.num_fct(), "H1SemiNorm: Function space does not contain"
        " a function with name " << cmp << ".");
  if  (weights.invalid()) {
    H1EnergyIntegrand<TGridFunction> integrand(gridFct, fct);
    return IntegrateSubsets(integrand, gridFct, subsets, quadOrder);
  } else {
    H1EnergyIntegrand<TGridFunction> integrand(gridFct, fct, weights);
    return IntegrateSubsets(integrand, gridFct, subsets, quadOrder);
  }
}
template <typename TGridFunction>
number H1EnergyNorm(TGridFunction& gridFct, const char* cmp, int quadOrder, const char* subsets=NULL,
        ConstSmartPtr<typename H1SemiIntegrand<TGridFunction>::weight_type> weights = SPNULL)
{
  return (sqrt(H1EnergyNorm2(gridFct, cmp, quadOrder, subsets, weights)));
}
 
template <typename TGridFunction>
number H1EnergyNorm(SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder,
    const char* subsets, ConstSmartPtr<typename H1SemiIntegrand<TGridFunction>::weight_type> weights = SPNULL)
{ return H1EnergyNorm(*spGridFct, cmp, quadOrder, subsets, weights); }
 
template <typename TGridFunction>
number H1EnergyNorm( SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder)
{ return H1EnergyNorm(spGridFct, cmp, quadOrder, NULL); }
 
template <typename TGridFunction>
number H1EnergyNorm( SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder,
    ConstSmartPtr<typename H1SemiIntegrand<TGridFunction>::weight_type> weights)
{ return H1EnergyNorm(spGridFct, cmp, quadOrder, NULL, weights); }
 
 
 
 
template <typename TGridFunction>
class H1EnergyDistIntegrand
    : public StdIntegrand<number, TGridFunction::dim, H1EnergyDistIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
    typedef typename H1SemiIntegrand<TGridFunction>::weight_type weight_type;
 
  private:
    ScalarGridFunctionData<TGridFunction> m_fineData;
    const int m_fineTopLevel;
 
    ScalarGridFunctionData<TGridFunction> m_coarseData;
    const int m_coarseTopLevel;
 
    SmartPtr<MultiGrid> m_spMG;
 
    ConstSmartPtr<weight_type> m_spWeight;
 
  public:
    H1EnergyDistIntegrand(TGridFunction& fineGridFct, size_t fineCmp,
              TGridFunction& coarseGridFct, size_t coarseCmp)
    : m_fineData(fineGridFct, fineCmp),
      m_fineTopLevel(fineGridFct.dof_distribution()->grid_level().level()),
      m_coarseData(coarseGridFct, coarseCmp),
      m_coarseTopLevel(coarseGridFct.dof_distribution()->grid_level().level()),
      m_spMG(fineGridFct.domain()->grid()),
      m_spWeight(new ConstUserNumber<TGridFunction::dim>(1.0))
    {
      if(m_fineTopLevel < m_coarseTopLevel)
        UG_THROW("H1EnergyDistIntegrand: fine and top level inverted.");
 
      if(m_fineData.domain().get() != m_coarseData.domain().get())
        UG_THROW("H1EnergyDistIntegrand: grid functions defined on different domains.");
    };
 
    H1EnergyDistIntegrand(TGridFunction& fineGridFct, size_t fineCmp,
              TGridFunction& coarseGridFct, size_t coarseCmp,
              ConstSmartPtr<weight_type> spWeight)
    : m_fineData(fineGridFct, fineCmp),
      m_fineTopLevel(fineGridFct.dof_distribution()->grid_level().level()),
      m_coarseData(coarseGridFct, coarseCmp),
      m_coarseTopLevel(coarseGridFct.dof_distribution()->grid_level().level()),
      m_spMG(fineGridFct.domain()->grid()),
      m_spWeight(spWeight)
    {
      if(m_fineTopLevel < m_coarseTopLevel)
        UG_THROW("H1EnergyDistIntegrand: fine and top level inverted.");
 
      if(m_fineData.domain().get() != m_coarseData.domain().get())
        UG_THROW("H1EnergyDistIntegrand: grid functions defined on different domains.");
    }
    virtual ~H1EnergyDistIntegrand(){}
 
    virtual void set_subset(int si)
    {
      if(!m_fineData.is_def_in_subset(si))
        UG_THROW("H1EnergyDistIntegrand: Grid function component"
            <<m_fineData.fct()<<" not defined on subset "<<si);
      if(!m_coarseData.is_def_in_subset(si))
        UG_THROW("H1EnergyDistIntegrand: Grid function component"
            <<m_coarseData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vFineGlobIP[],
                  GridObject* pFineElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vFineLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
      typedef typename TGridFunction::template dim_traits<elemDim>::grid_base_object Element;
 
      const TGridFunction &fineGridFct  = m_fineData.grid_function();
      const TGridFunction &coarseGridFct  = m_coarseData.grid_function();
 
      //  get coarse element
      GridObject* pCoarseElem = pFineElem;
      if(m_coarseTopLevel < m_fineTopLevel){
        int parentLevel = m_spMG->get_level(pCoarseElem);
        while(parentLevel > m_coarseTopLevel){
          pCoarseElem = m_spMG->get_parent(pCoarseElem);
          parentLevel = m_spMG->get_level(pCoarseElem);
        }
      }
 
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID fineROID = pFineElem->reference_object_id();
      const ReferenceObjectID coarseROID = pCoarseElem->reference_object_id();
 
    //  get corner coordinates
      std::vector<MathVector<worldDim> > vCornerCoarse;
      CollectCornerCoordinates(vCornerCoarse, *static_cast<Element*>(pCoarseElem), *m_coarseData.domain());
 
    //  get reference Mapping
      DimReferenceMapping<elemDim, worldDim>& map
        = ReferenceMappingProvider::get<elemDim, worldDim>(coarseROID, vCornerCoarse);
 
      std::vector<MathVector<elemDim> > vCoarseLocIP;
      vCoarseLocIP.resize(numIP);
      for(size_t ip = 0; ip < vCoarseLocIP.size(); ++ip) VecSet(vCoarseLocIP[ip], 0.0);
      map.global_to_local(&vCoarseLocIP[0], vFineGlobIP, numIP);
 
 
      // determine weights
      std::vector<typename weight_type::data_type> elemWeights(numIP, MathMatrix<worldDim, worldDim>());
      UG_ASSERT(m_spWeight.valid(), "H1SemiDistIntegrand::evaluate requires valid weights!");
 
      //  get local solution if needed
      if(m_spWeight->requires_grid_fct())
      {
 
        LocalIndices ind;
        LocalVector u;
        fineGridFct.indices(pFineElem, ind);  //  get global indices
        u.resize(ind);              //  adapt local algebra
        GetLocalVector(u, fineGridFct);     //  read local values of u
 
        //  compute data
        try{
          (*m_spWeight)(&elemWeights[0], vFineGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), pFineElem,
              vCornerCoords, vFineLocIP, numIP, &u, NULL);
        } UG_CATCH_THROW("H1SemiDistIntegrand: Cannot evaluate data.");
      }
      else
      {
        //  compute data
        try{
          (*m_spWeight)(&elemWeights[0], vFineGlobIP, 0.0, IIntegrand<number, worldDim>::subset(), numIP);
        } UG_CATCH_THROW("H1SemiDistIntegrand: Cannot evaluate data.");
      }
 
      try{
 
 
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rFineLSFS =
          LocalFiniteElementProvider::get<elemDim>(fineROID, m_fineData.id());
      const LocalShapeFunctionSet<elemDim>& rCoarseLSFS =
          LocalFiniteElementProvider::get<elemDim>(coarseROID, m_coarseData.id());
 
    //  get multiindices of element
      std::vector<DoFIndex> vFineMI, vCoarseMI;
      m_fineData.dof_indices(pFineElem, vFineMI);
      m_coarseData.dof_indices(pCoarseElem, vCoarseMI);
 
      std::vector<MathVector<elemDim> > vFineLocGradient(vFineMI.size());
      std::vector<MathVector<elemDim> > vCoarseLocGradient(vCoarseMI.size());
 
    //  loop all integration points
      for(size_t ip = 0; ip < numIP; ++ip)
      {
      //  compute shape gradients at ip
        rFineLSFS.grads(&vFineLocGradient[0], vFineLocIP[ip]);
        rCoarseLSFS.grads(&vCoarseLocGradient[0], vCoarseLocIP[ip]);
 
      //  compute approximated solutions at integration point
        number fineSolIP = 0.0;
        MathVector<elemDim> fineLocTmp(0.0);
        for(size_t sh = 0; sh < vFineMI.size(); ++sh)
        {
          const number val = DoFRef(fineGridFct, vFineMI[sh]);
          fineSolIP += val * rFineLSFS.shape(sh, vFineLocIP[ip]);
          VecScaleAppend(fineLocTmp, val, vFineLocGradient[sh]);
        }
 
        number coarseSolIP = 0.0;
        MathVector<elemDim> coarseLocTmp(0.0);
        for(size_t sh = 0; sh < vCoarseMI.size(); ++sh)
        {
          const number val = DoFRef(coarseGridFct, vCoarseMI[sh]);
          coarseSolIP += val * rCoarseLSFS.shape(sh, vCoarseLocIP[ip]);
          VecScaleAppend(coarseLocTmp, val, vCoarseLocGradient[sh]);
        }
 
      //  compute global D*gradient
        MathVector<worldDim> fineGradIP;
        MathMatrix<worldDim, elemDim> fineJTInv;
        Inverse(fineJTInv, vJT[ip]);
        MatVecMult(fineGradIP, fineJTInv, fineLocTmp);
        MatVecMult(fineLocTmp, elemWeights[ip], fineGradIP);
 
      //  compute global D*gradient
        MathVector<worldDim> coarseGradIP;
        MathMatrix<worldDim, elemDim> coarseJTInv;
        map.jacobian_transposed_inverse(coarseJTInv, vCoarseLocIP[ip]);
        MatVecMult(coarseGradIP, coarseJTInv, coarseLocTmp);
        MatVecMult(coarseLocTmp, elemWeights[ip], coarseGradIP);
 
      //  get squared difference
        vValue[ip] = VecDistanceSq(fineLocTmp, coarseLocTmp);
 
      }
 
      }
      UG_CATCH_THROW("H1EnergyDiffIntegrand::evaluate: trial space missing.");
    }
};
 
 
template <typename TGridFunction>
number H1EnergyDistance2(TGridFunction& spGridFct1, const char* cmp1,
    TGridFunction& spGridFct2, const char* cmp2,
        int quadOrder, const char* subsets,
    ConstSmartPtr<typename H1SemiDistIntegrand<TGridFunction>::weight_type> weights)
{
  return GridFunctionDistance2<H1EnergyDistIntegrand<TGridFunction>, TGridFunction>
    (spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, subsets, weights);
}
 
template <typename TGridFunction>
number H1EnergyDistance(TGridFunction& spGridFct1, const char* cmp1,
    TGridFunction& spGridFct2, const char* cmp2,
        int quadOrder, const char* subsets,
    ConstSmartPtr<typename H1SemiDistIntegrand<TGridFunction>::weight_type> weights)
{ return sqrt(H1EnergyDistance2(spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, subsets, weights)); }
 
template <typename TGridFunction>
number H1EnergyDistance2(TGridFunction& spGridFct1, const char* cmp1,
            TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, ConstSmartPtr<typename H1SemiDistIntegrand<TGridFunction>::weight_type > weights)
{ return H1EnergyDistance2(spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, NULL, weights); }
 
template <typename TGridFunction>
number H1EnergyDistance(TGridFunction& spGridFct1, const char* cmp1,
            TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, ConstSmartPtr<typename H1SemiDistIntegrand<TGridFunction>::weight_type > weights)
{ return sqrt(H1EnergyDistance2(spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, NULL, weights)); }
 
 
 
 
// H1 norm integrand
template <typename TGridFunction>
class H1NormIntegrand
  : public StdIntegrand<number, TGridFunction::dim, H1NormIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
 
  private:
    ScalarGridFunctionData<TGridFunction> m_scalarData;
 
  public:
    H1NormIntegrand(TGridFunction& gridFct, size_t cmp)
    : m_scalarData(gridFct, cmp) {}
 
    virtual ~H1NormIntegrand() {}
 
    virtual void set_subset(int si)
    {
      if(!m_scalarData.is_def_in_subset(si))
        UG_THROW("H1Norm: Grid function component"
            <<m_scalarData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID roid = pElem->reference_object_id();
 
      try{
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rTrialSpace =
              LocalFiniteElementProvider::get<elemDim>(roid, m_scalarData.id());
 
    //  number of dofs on element
      const size_t num_sh = rTrialSpace.num_sh();
 
    //  get multiindices of element
      std::vector<DoFIndex> ind;  //  aux. index array
      m_scalarData.dof_indices(pElem, ind);
 
    //  check multi indices
      if(ind.size() != num_sh)
        UG_THROW("H1ErrorIntegrand::evaluate: Wrong number of"
            " multi indices.");
 
    //  loop all integration points
      std::vector<MathVector<elemDim> > vLocGradient(num_sh);
      for(size_t ip = 0; ip < numIP; ++ip)
      {
 
      //  compute shape gradients at ip
        rTrialSpace.grads(&vLocGradient[0], vLocIP[ip]);
 
      //  compute approximated solution at integration point
        number approxSolIP = 0.0;
        MathVector<elemDim> locTmp; VecSet(locTmp, 0.0);
        for(size_t sh = 0; sh < num_sh; ++sh)
        {
        //  get value at shape point (e.g. corner for P1 fct)
          const number valSH = DoFRef(m_scalarData.grid_function(), ind[sh]);
 
        //  add shape fct at ip * value at shape
          approxSolIP += valSH * rTrialSpace.shape(sh, vLocIP[ip]);
 
        //  add gradient at ip
          VecScaleAppend(locTmp, valSH, vLocGradient[sh]);
        }
 
      //  compute global gradient
        MathVector<worldDim> approxGradIP;
        MathMatrix<worldDim, elemDim> JTInv;
        RightInverse(JTInv, vJT[ip]);
        MatVecMult(approxGradIP, JTInv, locTmp);
 
      //  get squared of difference
        vValue[ip] = approxSolIP * approxSolIP;
        vValue[ip] += VecDot(approxGradIP, approxGradIP);
      }
 
      }
      UG_CATCH_THROW("H1SemiNormFuncIntegrand::evaluate: trial space missing.");
    }
};
 
 
 
 
template <typename TGridFunction>
number H1Norm2(TGridFunction& u, const char* cmp,
         int quadOrder, const char* subsets=NULL)
{
//  get function id of name
  const size_t fct = u.fct_id_by_name(cmp);
 
//  check that function exists
  if(fct >= u.num_fct())
    UG_THROW("H1Norm: Function space does not contain"
        " a function with name " << cmp << ".");
 
  H1NormIntegrand<TGridFunction> spIntegrand(u, fct);
  return IntegrateSubsets(spIntegrand, u, subsets, quadOrder);
}
 
 
template <typename TGridFunction>
number H1Norm(TGridFunction& u, const char* cmp,
         int quadOrder, const char* subsets=NULL)
{
  return sqrt(H1Norm2(u, cmp, quadOrder,subsets));
}
 
template <typename TGridFunction>
number H1Norm(SmartPtr<TGridFunction> spGridFct, const char* cmp,
         int quadOrder, const char* subsets)
{
  return H1Norm(*spGridFct, cmp, quadOrder, subsets);
}
 
template <typename TGridFunction>
number H1Norm(SmartPtr<TGridFunction> spGridFct, const char* cmp, int quadOrder)
{
  return H1Norm(*spGridFct, cmp, quadOrder, NULL);
}
 
 
 
template <typename TGridFunction>
class H1DistIntegrand
  : public StdIntegrand<number, TGridFunction::dim, H1DistIntegrand<TGridFunction> >
{
  public:
    static const int worldDim = TGridFunction::dim;
 
  private:
    ScalarGridFunctionData<TGridFunction> m_fineData;
    const int m_fineTopLevel;
 
    ScalarGridFunctionData<TGridFunction> m_coarseData;
    const int m_coarseTopLevel;
 
    SmartPtr<MultiGrid> m_spMG;
 
  public:
    H1DistIntegrand(TGridFunction& fineGridFct, size_t fineCmp,
                    TGridFunction& coarseGridFct, size_t coarseCmp)
    : m_fineData(fineGridFct, fineCmp),
      m_fineTopLevel(fineGridFct.dof_distribution()->grid_level().level()),
      m_coarseData(coarseGridFct, coarseCmp),
      m_coarseTopLevel(coarseGridFct.dof_distribution()->grid_level().level()),
      m_spMG(fineGridFct.domain()->grid())
    {
      if(m_fineTopLevel < m_coarseTopLevel)
        UG_THROW("H1DiffIntegrand: fine and top level inverted.");
 
      if(fineGridFct.domain().get() !=
          coarseGridFct.domain().get())
        UG_THROW("H1DiffIntegrand: grid functions defined on different domains.");
    };
 
    virtual ~H1DistIntegrand() {};
 
    virtual void set_subset(int si)
    {
      if(!m_fineData.is_def_in_subset(si))
        UG_THROW("H1DiffIntegrand: Grid function component"
            <<m_fineData.fct()<<" not defined on subset "<<si);
      if(!m_coarseData.is_def_in_subset(si))
        UG_THROW("H1DiffIntegrand: Grid function component"
            <<m_coarseData.fct()<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vFineGlobIP[],
                  GridObject* pFineElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vFineLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
      typedef typename TGridFunction::template dim_traits<elemDim>::grid_base_object Element;
 
      //  get coarse element
      GridObject* pCoarseElem = pFineElem;
      if(m_coarseTopLevel < m_fineTopLevel){
        int parentLevel = m_spMG->get_level(pCoarseElem);
        while(parentLevel > m_coarseTopLevel){
          pCoarseElem = m_spMG->get_parent(pCoarseElem);
          parentLevel = m_spMG->get_level(pCoarseElem);
        }
      }
 
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      const ReferenceObjectID fineROID = pFineElem->reference_object_id();
      const ReferenceObjectID coarseROID = pCoarseElem->reference_object_id();
 
    //  get corner coordinates
      std::vector<MathVector<worldDim> > vCornerCoarse;
      CollectCornerCoordinates(vCornerCoarse, *static_cast<Element*>(pCoarseElem), *m_coarseData.domain());
 
    //  get Reference Mapping
      DimReferenceMapping<elemDim, worldDim>& map
        = ReferenceMappingProvider::get<elemDim, worldDim>(coarseROID, vCornerCoarse);
 
      std::vector<MathVector<elemDim> > vCoarseLocIP;
      vCoarseLocIP.resize(numIP);
      for(size_t ip = 0; ip < vCoarseLocIP.size(); ++ip) VecSet(vCoarseLocIP[ip], 0.0);
      map.global_to_local(&vCoarseLocIP[0], vFineGlobIP, numIP);
 
      try{
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rFineLSFS =
          LocalFiniteElementProvider::get<elemDim>(fineROID, m_fineData.id());
      const LocalShapeFunctionSet<elemDim>& rCoarseLSFS =
          LocalFiniteElementProvider::get<elemDim>(coarseROID, m_coarseData.id());
 
    //  get multiindices of element
      std::vector<DoFIndex> vFineMI, vCoarseMI;
      m_fineData.dof_indices(pFineElem, vFineMI);
      m_coarseData.dof_indices(pCoarseElem, vCoarseMI);
 
      std::vector<MathVector<elemDim> > vFineLocGradient(vFineMI.size());
      std::vector<MathVector<elemDim> > vCoarseLocGradient(vCoarseMI.size());
 
    //  loop all integration points
      for(size_t ip = 0; ip < numIP; ++ip)
      {
      //  compute shape gradients at ip
        rFineLSFS.grads(&vFineLocGradient[0], vFineLocIP[ip]);
        rCoarseLSFS.grads(&vCoarseLocGradient[0], vCoarseLocIP[ip]);
 
      //  compute approximated solution at integration point
        number fineSolIP = 0.0;
        MathVector<elemDim> fineLocTmp; VecSet(fineLocTmp, 0.0);
        for(size_t sh = 0; sh < vFineMI.size(); ++sh)
        {
          const number val = DoFRef(m_fineData.grid_function(), vFineMI[sh]);
          fineSolIP += val * rFineLSFS.shape(sh, vFineLocIP[ip]);
          VecScaleAppend(fineLocTmp, val, vFineLocGradient[sh]);
        }
        number coarseSolIP = 0.0;
        MathVector<elemDim> coarseLocTmp; VecSet(coarseLocTmp, 0.0);
        for(size_t sh = 0; sh < vCoarseMI.size(); ++sh)
        {
          const number val = DoFRef(m_coarseData.grid_function(), vCoarseMI[sh]);
          coarseSolIP += val * rCoarseLSFS.shape(sh, vCoarseLocIP[ip]);
          VecScaleAppend(coarseLocTmp, val, vCoarseLocGradient[sh]);
        }
 
      //  compute global gradient
        MathVector<worldDim> fineGradIP;
        MathMatrix<worldDim, elemDim> fineJTInv;
        RightInverse(fineJTInv, vJT[ip]);
        MatVecMult(fineGradIP, fineJTInv, fineLocTmp);
 
      //  compute global gradient
        MathVector<worldDim> coarseGradIP;
        MathMatrix<worldDim, elemDim> coarseJTInv;
        map.jacobian_transposed_inverse(coarseJTInv, vCoarseLocIP[ip]);
        MatVecMult(coarseGradIP, coarseJTInv, coarseLocTmp);
 
      //  get squared of difference
        vValue[ip] = (coarseSolIP - fineSolIP);
        vValue[ip] *= vValue[ip];
        vValue[ip] += VecDistanceSq(coarseGradIP, fineGradIP);
      }
 
      }
      UG_CATCH_THROW("H1DiffIntegrand::evaluate: trial space missing.");
    }
};
 
 
 
template <typename TGridFunction>
number H1Distance2(TGridFunction& spGridFct1, const char* cmp1,
               TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets=NULL)
{
  return GridFunctionDistance2<H1DistIntegrand<TGridFunction>, TGridFunction>
    (spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, subsets);
}
 
 
template <typename TGridFunction>
number H1Distance(TGridFunction& spGridFct1, const char* cmp1,
               TGridFunction& spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets=NULL)
{
  return sqrt(H1Distance2(spGridFct1, cmp1, spGridFct2, cmp2, quadOrder, subsets));
}
template <typename TGridFunction>
number H1Error(SmartPtr<TGridFunction> spGridFct1, const char* cmp1,
               SmartPtr<TGridFunction> spGridFct2, const char* cmp2,
               int quadOrder, const char* subsets)
{
  return H1Distance(*spGridFct1, cmp1, *spGridFct2, cmp2, quadOrder, subsets);
}
 
template <typename TGridFunction>
number H1Error(SmartPtr<TGridFunction> spGridFct1, const char* cmp1,
               SmartPtr<TGridFunction> spGridFct2, const char* cmp2,
               int quadOrder)
{
  return H1Distance(*spGridFct1, cmp1, *spGridFct2, cmp2, quadOrder, NULL);
}
 
 
// Standard Integrand
 
template <typename TGridFunction>
class StdFuncIntegrand
  : public StdIntegrand<number, TGridFunction::dim, StdFuncIntegrand<TGridFunction> >
{
  public:
  //  world dimension of grid function
    static const int worldDim = TGridFunction::dim;
 
  private:
  // grid function
    TGridFunction* m_pGridFct;
 
  //  component of function
    const size_t m_fct;
 
  public:
    StdFuncIntegrand(TGridFunction* pGridFct, size_t cmp)
    : m_pGridFct(pGridFct), m_fct(cmp)
    {};
 
    virtual ~StdFuncIntegrand(){}
 
    virtual void set_subset(int si)
    {
      if(!m_pGridFct->is_def_in_subset(m_fct, si))
        UG_THROW("L2ErrorIntegrand: Grid function component"
            <<m_fct<<" not defined on subset "<<si);
      IIntegrand<number, worldDim>::set_subset(si);
    }
 
    template <int elemDim>
    void evaluate(number vValue[],
                  const MathVector<worldDim> vGlobIP[],
                  GridObject* pElem,
                  const MathVector<worldDim> vCornerCoords[],
                  const MathVector<elemDim> vLocIP[],
                  const MathMatrix<elemDim, worldDim> vJT[],
                  const size_t numIP)
    {
    //  get reference object id (i.e. Triangle, Quadrilateral, Tetrahedron, ...)
      ReferenceObjectID roid = (ReferenceObjectID) pElem->reference_object_id();
 
      const LFEID m_id = m_pGridFct->local_finite_element_id(m_fct);
 
      try{
    //  get trial space
      const LocalShapeFunctionSet<elemDim>& rTrialSpace =
              LocalFiniteElementProvider::get<elemDim>(roid, m_id);
 
    //  number of dofs on element
      const size_t num_sh = rTrialSpace.num_sh();
 
    //  get multiindices of element
 
      std::vector<DoFIndex> ind;  //  aux. index array
      m_pGridFct->dof_indices(pElem, m_fct, ind);
 
    //  check multi indices
      UG_COND_THROW(ind.size() != num_sh,
            "StdFuncIntegrand::evaluate: Wrong number of multi indices.");
 
    //  loop all integration points
      for(size_t ip = 0; ip < numIP; ++ip)
      {
 
      //  compute approximated solution at integration point
        number approxSolIP = 0.0;
        for(size_t sh = 0; sh < num_sh; ++sh)
        {
          //  get value at shape point (e.g. corner for P1 fct)
          //  and add shape fct at ip * value at shape
          const number valSH = DoFRef((*m_pGridFct), ind[sh]);
          approxSolIP += valSH * rTrialSpace.shape(sh, vLocIP[ip]);
        }
 
        //  get function value at ip
        vValue[ip] = approxSolIP;
 
      }
 
      }
      UG_CATCH_THROW("StdFuncIntegrand::evaluate: trial space missing.");
    }
};
 
 
template <typename TGridFunction>
number StdFuncIntegralOnVertex(TGridFunction& gridFct,
                 size_t fct,
                 int si)
{
//  integrate elements of subset
  typedef typename TGridFunction::template dim_traits<0>::grid_base_object grid_base_object;
  typedef typename TGridFunction::template dim_traits<0>::const_iterator const_iterator;
 
  //  reset the result
  number integral = 0;
 
//  note: this iterator is for the base elements, e.g. Face and not
//      for the special type, e.g. Triangle, Quadrilateral
  const_iterator iter = gridFct.template begin<grid_base_object>(si);
  const_iterator iterEnd = gridFct.template end<grid_base_object>(si);
 
//  iterate over all elements
  for(; iter != iterEnd; ++iter)
  {
  //  get element
    grid_base_object* pElem = *iter;
 
    std::vector<DoFIndex> ind;  //  aux. index array
    gridFct.dof_indices(pElem, fct, ind);
 
  //  compute approximated solution at integration point
    number value = 0.0;
    for(size_t sh = 0; sh < ind.size(); ++sh)
    {
      value += DoFRef(gridFct, ind[sh]);
    }
 
  //  add to global sum
    integral += value;
 
  } // end elem
 
//  return the summed integral contributions of all elements
  return integral;
}
 
template <typename TGridFunction>
number StdFuncIntegralOnVertex(SmartPtr<TGridFunction> spGridFct, size_t fct, int si)
{ return StdFuncIntegralOnVertex(*spGridFct, fct, si); }
 
 
template <typename TGridFunction>
number Integral(TGridFunction& gridFct, const char* cmp,
                const char* subsets, int quadOrder)
{
//  get function id of name
  const size_t fct = gridFct.fct_id_by_name(cmp);
 
//  check that function exists
  UG_COND_THROW(fct >= gridFct.num_fct(), "L2Norm: Function space does not contain"
        " a function with name " << cmp << ".");
 
//  read subsets
  SubsetGroup ssGrp(gridFct.domain()->subset_handler());
  if(subsets != NULL)
  {
    ssGrp.add(TokenizeString(subsets));
    if(!SameDimensionsInAllSubsets(ssGrp))
      UG_THROW("IntegrateSubsets: Subsets '"<<subsets<<"' do not have same dimension."
           "Can not integrate on subsets of different dimensions.");
  }
  else
  {
  //  add all subsets and remove lower dim subsets afterwards
    ssGrp.add_all();
    RemoveLowerDimSubsets(ssGrp);
  }
 
  // \TODO: This should be generalite in IntegrateSubset instead of doing it directly here
  bool bOnlyVertex = true;
  for(size_t s = 0; s < ssGrp.size(); ++s)
    if(ssGrp.dim(s) != 0) bOnlyVertex = false;
 
  if(bOnlyVertex)
  {
    number value = 0;
    for(size_t s = 0; s < ssGrp.size(); ++s)
      value += StdFuncIntegralOnVertex(gridFct, fct, ssGrp[s]);
 
#ifdef UG_PARALLEL
  // sum over processes
  if(pcl::NumProcs() > 1)
  {
    pcl::ProcessCommunicator com;
    number local = value;
    com.allreduce(&local, &value, 1, PCL_DT_DOUBLE, PCL_RO_SUM);
  }
#endif
    return value;
  }
 
  StdFuncIntegrand<TGridFunction> integrand(&gridFct, fct);
  return IntegrateSubsets(integrand, gridFct, subsets, quadOrder);
}
 
template <typename TGridFunction>
number Integral(SmartPtr<TGridFunction> spGridFct, const char* cmp,
                const char* subsets, int quadOrder)
{ return Integral(*spGridFct, cmp, subsets, quadOrder); }
 
 
template <typename TGridFunction>
number Integral(SmartPtr<TGridFunction> spGridFct, const char* cmp,
                const char* subsets)
{
  return Integral(spGridFct, cmp, subsets, 1);
}
template <typename TGridFunction>
number Integral(SmartPtr<TGridFunction> spGridFct, const char* cmp)
{
  return Integral(spGridFct, cmp, NULL, 1);
}
 
 
// Generic Boundary Integration Routine
 
template <int WorldDim, int dim, typename TConstIterator>
number IntegralNormalComponentOnManifoldUsingFV1Geom(TConstIterator iterBegin,
                                       TConstIterator iterEnd,
                                       typename domain_traits<WorldDim>::position_accessor_type& aaPos,
                                       const ISubsetHandler* ish,
                                       IIntegrand<MathVector<WorldDim>, WorldDim>& integrand,
                                       const SubsetGroup& bndSSGrp)
{
//  reset the result
  number integral = 0;
 
//  note: this iterator is for the base elements, e.g. Face and not
//      for the special type, e.g. Triangle, Quadrilateral
  TConstIterator iter = iterBegin;
 
//  this is the base element type (e.g. Face). This is the type when the
//  iterators above are dereferenciated.
  typedef typename domain_traits<dim>::grid_base_object grid_base_object;
 
//  create a FV1 Geometry
  DimFV1Geometry<dim> geo;
 
//  specify, which subsets are boundary
  for(size_t s = 0; s < bndSSGrp.size(); ++s)
  {
  //  get subset index
    const int bndSubset = bndSSGrp[s];
 
  //  request this subset index as boundary subset. This will force the
  //  creation of boundary subsets when calling geo.update
    geo.add_boundary_subset(bndSubset);
  }
 
//  vector of corner coordinates of element corners (to be filled for each elem)
  std::vector<MathVector<WorldDim> > vCorner;
 
//  iterate over all elements
  for(; iter != iterEnd; ++iter)
  {
  //  get element
    grid_base_object* pElem = *iter;
 
  //  get all corner coordinates
    CollectCornerCoordinates(vCorner, *pElem, aaPos, true);
 
  //  compute bf and grads at bip for element
    try{
      geo.update(pElem, &vCorner[0], ish);
    }
    UG_CATCH_THROW("IntegralNormalComponentOnManifold: "
          "Cannot update Finite Volume Geometry.");
 
  //  specify, which subsets are boundary
    for(size_t s = 0; s < bndSSGrp.size(); ++s)
    {
    //  get subset index
      const int bndSubset = bndSSGrp[s];
 
    //  get all bf of this subset
      typedef typename DimFV1Geometry<dim>::BF BF;
      const std::vector<BF>& vBF = geo.bf(bndSubset);
 
    //  loop boundary faces
      for(size_t b = 0; b < vBF.size(); ++b)
      {
      //  get bf
        const BF& bf = vBF[b];
 
      //  value
        MathVector<WorldDim> value;
 
      //  jacobian
        MathMatrix<dim, WorldDim> JT;
        Inverse(JT, bf.JTInv());
 
      //  compute integrand values at integration points
        try
        {
          integrand.values(&value, &(bf.global_ip()),
                   pElem, &vCorner[0], &(bf.local_ip()),
                   &(JT),
                   1);
        }
        UG_CATCH_THROW("IntegralNormalComponentOnManifold: Unable to compute values of "
                "integrand at integration point.");
 
      //  sum up contribution (normal includes area)
        integral += VecDot(value, bf.normal());
 
      } // end bf
    } // end bnd subsets
  } // end elem
 
//  return the summed integral contributions of all elements
  return integral;
}
 
 
template <int WorldDim, int dim, typename TConstIterator>
number IntegralNormalComponentOnManifoldGeneral(
    TConstIterator iterBegin,
    TConstIterator iterEnd,
    typename domain_traits<WorldDim>::position_accessor_type& aaPos,
    const ISubsetHandler* ish,
    IIntegrand<MathVector<WorldDim>, WorldDim>& integrand,
    const SubsetGroup& bndSSGrp,
    int quadOrder,
    Grid& grid)
{
//  reset the result
  number integral = 0;
 
//  note: this iterator is for the base elements, e.g. Face and not
//      for the special type, e.g. Triangle, Quadrilateral
  TConstIterator iter = iterBegin;
 
//  this is the base element type (e.g. Face). This is the type when the
//  iterators above are dereferenciated.
  typedef typename domain_traits<dim>::element_type Element;
  typedef typename domain_traits<dim>::side_type Side;
 
//  vector of corner coordinates of element corners (to be filled for each elem)
  std::vector<MathVector<WorldDim> > vCorner;
  std::vector<int> vSubsetIndex;
 
//  iterate over all elements
  for(; iter != iterEnd; ++iter)
  {
  //  get element
    Element* pElem = *iter;
 
  //  get all corner coordinates
    CollectCornerCoordinates(vCorner, *pElem, aaPos, true);
 
  //  get reference object id
    const ReferenceObjectID elemRoid = pElem->reference_object_id();
 
  //  get sides
    typename Grid::traits<Side>::secure_container vSide;
    grid.associated_elements_sorted(vSide, pElem);
    vSubsetIndex.resize(vSide.size());
    for(size_t i = 0; i < vSide.size(); ++i)
      vSubsetIndex[i] = ish->get_subset_index(vSide[i]);
 
    DimReferenceMapping<dim, WorldDim>& rMapping
      = ReferenceMappingProvider::get<dim, WorldDim>(elemRoid, vCorner);
 
    const DimReferenceElement<dim>& rRefElem
      = ReferenceElementProvider::get<dim>(elemRoid);
 
  //  loop sub elements
    for(size_t side = 0; side < vSide.size(); ++side)
    {
    //  check if side used
      if(!bndSSGrp.contains(vSubsetIndex[side])) continue;
 
    //  get side
      Side* pSide = vSide[side];
 
      std::vector<MathVector<WorldDim> > vSideCorner(rRefElem.num(dim-1, side, 0));
      std::vector<MathVector<dim> > vLocalSideCorner(rRefElem.num(dim-1, side, 0));
      for(size_t co = 0; co < vSideCorner.size(); ++co){
        vSideCorner[co] = vCorner[rRefElem.id(dim-1, side, 0, co)];
        vLocalSideCorner[co] = rRefElem.corner(rRefElem.id(dim-1, side, 0, co));
      }
 
    //  side quad rule
      const ReferenceObjectID sideRoid = pSide->reference_object_id();
      const QuadratureRule<dim-1>& rSideQuadRule
          = QuadratureRuleProvider<dim-1>::get(sideRoid, quadOrder);
 
    //  normal
      MathVector<WorldDim> Normal;
      ElementNormal<WorldDim>(sideRoid, Normal, &vSideCorner[0]);
 
    //  quadrature points
      const number* vWeight = rSideQuadRule.weights();
      const size_t nip = rSideQuadRule.size();
      std::vector<MathVector<dim> > vLocalIP(nip);
      std::vector<MathVector<dim> > vGlobalIP(nip);
 
      DimReferenceMapping<dim-1, dim>& map
        = ReferenceMappingProvider::get<dim-1, dim>(sideRoid, vLocalSideCorner);
 
      for(size_t ip = 0; ip < nip; ++ip)
        map.local_to_global(vLocalIP[ip], rSideQuadRule.point(ip));
 
      for(size_t ip = 0; ip < nip; ++ip)
        rMapping.local_to_global(vGlobalIP[ip], vLocalIP[ip]);
 
    //  compute transformation matrices
      std::vector<MathMatrix<dim-1, WorldDim> > vJT(nip);
      map.jacobian_transposed(&(vJT[0]), rSideQuadRule.points(), nip);
 
      std::vector<MathMatrix<dim, WorldDim> > vElemJT(nip);
      rMapping.jacobian_transposed(&(vElemJT[0]), &vLocalIP[0], nip);
 
      std::vector<MathVector<WorldDim> > vValue(nip);
 
    //  compute integrand values at integration points
      try
      {
        integrand.values(&vValue[0], &vGlobalIP[0],
                 pElem, &vCorner[0], &vLocalIP[0],
                 &(vElemJT[0]),
                 nip);
      }
      UG_CATCH_THROW("IntegralNormalComponentOnManifold: Unable to compute values of "
              "integrand at integration point.");
 
    //  loop integration points
      for(size_t ip = 0; ip < nip; ++ip)
      {
      //  get quadrature weight
        const number weightIP = vWeight[ip];
 
      //  get determinate of mapping
        const number det = SqrtGramDeterminant(vJT[ip]);
 
      //  add contribution of integration point
        integral +=  VecDot(vValue[ip], Normal) * weightIP * det;
      }
    } // end bf
  } // end elem
 
//  return the summed integral contributions of all elements
  return integral;
}
 
template <typename TGridFunction, int dim>
number IntegralNormalComponentOnManifoldSubset(SmartPtr<IIntegrand<MathVector<TGridFunction::dim>, TGridFunction::dim> > spIntegrand,
                                 SmartPtr<TGridFunction> spGridFct,
                                 int si, const SubsetGroup& bndSSGrp, int quadOrder)
{
//  integrate elements of subset
  typedef typename TGridFunction::template dim_traits<dim>::grid_base_object grid_base_object;
  typedef typename TGridFunction::template dim_traits<dim>::const_iterator const_iterator;
  static const int WorldDim = TGridFunction::dim;
 
  spIntegrand->set_subset(si);
 
  if(quadOrder == 1)
    return IntegralNormalComponentOnManifoldUsingFV1Geom<WorldDim,dim,const_iterator>
          (spGridFct->template begin<grid_base_object>(si),
                   spGridFct->template end<grid_base_object>(si),
                   spGridFct->domain()->position_accessor(),
                   spGridFct->domain()->subset_handler().get(),
                   *spIntegrand, bndSSGrp);
  else{
    UG_LOG(" #### IntegralNormalComponentOnManifoldSubset ####:\n")
    return IntegralNormalComponentOnManifoldGeneral<WorldDim,dim,const_iterator>
          (spGridFct->template begin<grid_base_object>(si),
                   spGridFct->template end<grid_base_object>(si),
                   spGridFct->domain()->position_accessor(),
                   spGridFct->domain()->subset_handler().get(),
                   *spIntegrand, bndSSGrp, quadOrder, *spGridFct->domain()->grid());
  }
}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifoldSubsets(
    SmartPtr<IIntegrand<MathVector<TGridFunction::dim>, TGridFunction::dim> > spIntegrand,
    SmartPtr<TGridFunction> spGridFct,
    const char* BndSubsets, const char* InnerSubsets,
    int quadOrder)
{
//  world dimensions
  static const int dim = TGridFunction::dim;
 
//  read subsets
  SubsetGroup innerSSGrp(spGridFct->domain()->subset_handler());
  if(InnerSubsets != NULL)
  {
    innerSSGrp.add(TokenizeString(InnerSubsets));
    if(!SameDimensionsInAllSubsets(innerSSGrp))
      UG_THROW("IntegralNormalComponentOnManifold: Subsets '"<<InnerSubsets<<"' do not have same dimension."
               "Can not integrate on subsets of different dimensions.");
  }
  else
  {
  //  add all subsets and remove lower dim subsets afterwards
    innerSSGrp.add_all();
    RemoveLowerDimSubsets(innerSSGrp);
  }
 
//  read subsets
  SubsetGroup bndSSGrp(spGridFct->domain()->subset_handler());
  if(BndSubsets != NULL)
    bndSSGrp.add(TokenizeString(BndSubsets));
  else
    UG_THROW("IntegralNormalComponentOnManifold: No boundary subsets passed.");
 
//  reset value
  number value = 0;
 
//  loop subsets
  for(size_t i = 0; i < innerSSGrp.size(); ++i)
  {
  //  get subset index
    const int si = innerSSGrp[i];
 
  //  check dimension
    if(innerSSGrp.dim(i) != dim && innerSSGrp.dim(i) != DIM_SUBSET_EMPTY_GRID)
      UG_THROW("IntegralNormalComponentOnManifold: Dimension of inner subset is "<<
               innerSSGrp.dim(i)<<", but only World Dimension "<<dim<<
               " subsets can be used for inner subsets.");
 
  //  integrate elements of subset
    switch(innerSSGrp.dim(i))
    {
      case DIM_SUBSET_EMPTY_GRID: break;
      case dim: value += IntegralNormalComponentOnManifoldSubset<TGridFunction, dim>(spIntegrand, spGridFct, si, bndSSGrp, quadOrder); break;
      default: UG_THROW("IntegralNormalComponentOnManifold: Dimension "<<innerSSGrp.dim(i)<<" not supported. "
                        " World dimension is "<<dim<<".");
    }
  }
 
#ifdef UG_PARALLEL
  // sum over processes
  if(pcl::NumProcs() > 1)
  {
    pcl::ProcessCommunicator com;
    number local = value;
    com.allreduce(&local, &value, 1, PCL_DT_DOUBLE, PCL_RO_SUM);
  }
#endif
 
//  return the result
  return value;
}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    SmartPtr<UserData<MathVector<TGridFunction::dim>, TGridFunction::dim> > spData,
    SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset, const char* InnerSubset,
    number time,
    int quadOrder)
{
  SmartPtr<IIntegrand<MathVector<TGridFunction::dim>, TGridFunction::dim> > spIntegrand
    = make_sp(new UserDataIntegrand<MathVector<TGridFunction::dim>, TGridFunction>(spData, &(*spGridFct), time));
 
  return IntegralNormalComponentOnManifoldSubsets(spIntegrand, spGridFct, BndSubset, InnerSubset, quadOrder);
}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    SmartPtr<UserData<MathVector<TGridFunction::dim>, TGridFunction::dim> > spData,
    SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset, const char* InnerSubset,
    number time)
{return IntegralNormalComponentOnManifold(spData, spGridFct, BndSubset, InnerSubset, time, 1);}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    SmartPtr<UserData<MathVector<TGridFunction::dim>, TGridFunction::dim> > spData,
    SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset,
    number time)
{return IntegralNormalComponentOnManifold(spData, spGridFct, BndSubset, NULL, time, 1);}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    SmartPtr<UserData<MathVector<TGridFunction::dim>, TGridFunction::dim> > spData,
    SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset, const char* InnerSubset)
{return IntegralNormalComponentOnManifold(spData, spGridFct, BndSubset, InnerSubset, 0.0, 1);}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    SmartPtr<UserData<MathVector<TGridFunction::dim>, TGridFunction::dim> > spData,
    SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset)
{return IntegralNormalComponentOnManifold(spData, spGridFct, BndSubset, NULL, 0.0, 1);}
 
// lua data
 
#ifdef UG_FOR_LUA
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    const char* luaFct, SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset, const char* InnerSubset,
    number time, int quadOrder)
{
  static const int dim = TGridFunction::dim;
  SmartPtr<UserData<MathVector<dim>, dim> > sp =
      LuaUserDataFactory<MathVector<dim>, dim>::create(luaFct);
  return IntegralNormalComponentOnManifold(sp, spGridFct, BndSubset, InnerSubset, time, quadOrder);
}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    const char* luaFct, SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset, const char* InnerSubset,
    number time)
{return IntegralNormalComponentOnManifold(luaFct, spGridFct, BndSubset, InnerSubset, time, 1);}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    const char* luaFct, SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset,
    number time)
{return IntegralNormalComponentOnManifold(luaFct, spGridFct, BndSubset, NULL, time, 1);}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    const char* luaFct, SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset, const char* InnerSubset)
{return IntegralNormalComponentOnManifold(luaFct, spGridFct, BndSubset, InnerSubset, 0.0, 1);}
 
template <typename TGridFunction>
number IntegralNormalComponentOnManifold(
    const char* luaFct, SmartPtr<TGridFunction> spGridFct,
    const char* BndSubset)
{return IntegralNormalComponentOnManifold(luaFct, spGridFct, BndSubset, NULL, 0.0, 1);}
#endif
 
// Boundary Integral
 
template <typename TGridFunction>
number IntegrateNormalComponentOnManifold(TGridFunction& u, const char* cmp,
                                   const char* BndSubset)
{
//  get function id of name
  const size_t fct = u.fct_id_by_name(cmp);
 
//  check that function exists
  if(fct >= u.num_fct())
    UG_THROW("IntegrateNormalComponentOnManifold: Function space does not contain"
        " a function with name " << cmp << ".");
 
  if(u.local_finite_element_id(fct) != LFEID(LFEID::LAGRANGE, TGridFunction::dim, 1))
    UG_THROW("IntegrateNormalComponentOnManifold:"
         "Only implemented for Lagrange P1 functions.");
 
//  read bnd subsets
  SubsetGroup bndSSGrp(u.domain()->subset_handler());
  bndSSGrp.add(TokenizeString(BndSubset));
 
//  reset value
  number value = 0;
 
//  loop subsets
  for(size_t i = 0; i < bndSSGrp.size(); ++i)
  {
  //  get subset index
    const int si = bndSSGrp[i];
 
  //  skip if function is not defined in subset
    if(!u.is_def_in_subset(fct, si)) continue;
 
  //  create integration kernel
    static const int dim = TGridFunction::dim;
 
  //  integrate elements of subset
    typedef typename domain_traits<dim>::grid_base_object grid_base_object;
 
  //  get iterators for all elems on subset
    typedef typename TGridFunction::template dim_traits<dim>::const_iterator const_iterator;
    const_iterator iter = u.template begin<grid_base_object>();
    const_iterator iterEnd = u.template end<grid_base_object>();
 
  //  create a FV1 Geometry
    DimFV1Geometry<dim> geo;
 
  //  specify, which subsets are boundary
    for(size_t s = 0; s < bndSSGrp.size(); ++s)
    {
    //  get subset index
      const int bndSubset = bndSSGrp[s];
 
    //  request this subset index as boundary subset. This will force the
    //  creation of boundary subsets when calling geo.update
      geo.add_boundary_subset(bndSubset);
    }
 
  //  vector of corner coordinates of element corners (to be filled for each elem)
    std::vector<MathVector<dim> > vCorner;
 
  //  loop elements of subset
    for( ; iter != iterEnd; ++iter)
    {
    //  get element
      grid_base_object* elem = *iter;
 
    //  get all corner coordinates
      CollectCornerCoordinates(vCorner, *elem, u.domain()->position_accessor(), true);
 
    //  compute bf and grads at bip for element
      try{
        geo.update(elem, &vCorner[0], u.domain()->subset_handler().get());
      }
      UG_CATCH_THROW("IntegrateNormalComponenOnManifold: "
            "Cannot update Finite Volume Geometry.");
 
    //  get fct multi-indices of element
      std::vector<DoFIndex> ind;
      u.dof_indices(elem, fct, ind);
 
    //  specify, which subsets are boundary
      for(size_t s = 0; s < bndSSGrp.size(); ++s)
      {
      //  get subset index
        const int bndSubset = bndSSGrp[s];
 
      //  get all bf of this subset
        typedef typename DimFV1Geometry<dim>::BF BF;
        const std::vector<BF>& vBF = geo.bf(bndSubset);
 
      //  loop boundary faces
        for(size_t b = 0; b < vBF.size(); ++b)
        {
        //  get bf
          const BF& bf = vBF[b];
 
        //  get normal on bf
          const MathVector<dim>& normal = bf.normal();
 
        //  check multi indices
          UG_ASSERT(ind.size() == bf.num_sh(),
                    "IntegrateNormalComponentOnManifold::values: Wrong number of"
                " multi indices, ind: "<<ind.size() << ", bf.num_sh: "
                << bf.num_sh());
 
          MathVector<dim> val; VecSet(val, 0.0);
          for(size_t sh = 0; sh < bf.num_sh(); ++sh)
          {
            const number fctVal = DoFRef(u, ind[sh]);
              const MathVector<dim>& ip = bf.global_ip();
            VecScaleAdd(val, 1.0, val, fctVal, ip);
          }
 
          //  sum up contributions
          value -= VecDot(val, normal);
        }
      }
    }
  }
 
#ifdef UG_PARALLEL
  // sum over processes
  if(pcl::NumProcs() > 1)
  {
    pcl::ProcessCommunicator com;
    number local = value;
    com.allreduce(&local, &value, 1, PCL_DT_DOUBLE, PCL_RO_SUM);
  }
#endif
 
//  return the result
  return value;
}
 
 
template <typename TGridFunction>
number IntegrateNormalGradientOnManifold(TGridFunction& u, const char* cmp,
                                   const char* BndSubset, const char* InnerSubset = NULL)
{
//  get function id of name
  const size_t fct = u.fct_id_by_name(cmp);
 
//  check that function exists
  if(fct >= u.num_fct())
    UG_THROW("IntegrateNormalGradientOnManifold: Function space does not contain"
        " a function with name " << cmp << ".");
 
  if(u.local_finite_element_id(fct) != LFEID(LFEID::LAGRANGE, TGridFunction::dim, 1))
    UG_THROW("IntegrateNormalGradientOnManifold:"
         "Only implemented for Lagrange P1 functions.");
 
//  read subsets
  SubsetGroup innerSSGrp(u.domain()->subset_handler());
  if(InnerSubset != NULL)
    innerSSGrp.add(TokenizeString(InnerSubset));
  else // add all if no subset specified
    innerSSGrp.add_all();
 
//  read bnd subsets
  SubsetGroup bndSSGrp(u.domain()->subset_handler());
  if(InnerSubset != NULL){
    bndSSGrp.add(TokenizeString(BndSubset));
  }
  else{
    UG_THROW("IntegrateNormalGradientOnManifold: No boundary subsets specified. Aborting.");
  }
 
//  reset value
  number value = 0;
 
//  loop subsets
  for(size_t i = 0; i < innerSSGrp.size(); ++i)
  {
  //  get subset index
    const int si = innerSSGrp[i];
 
  //  skip if function is not defined in subset
    if(!u.is_def_in_subset(fct, si)) continue;
 
 
    if (innerSSGrp.dim(i) != TGridFunction::dim)
      UG_THROW("IntegrateNormalGradientOnManifold: Element dimension does not match world dimension!");
 
  //  create integration kernel
    static const int dim = TGridFunction::dim;
 
  //  integrate elements of subset
    typedef typename domain_traits<dim>::grid_base_object grid_base_object;
 
  //  get iterators for all elems on subset
    typedef typename TGridFunction::template dim_traits<dim>::const_iterator const_iterator;
    const_iterator iter = u.template begin<grid_base_object>();
    const_iterator iterEnd = u.template end<grid_base_object>();
 
  //  create a FV1 Geometry
    DimFV1Geometry<dim> geo;
 
  //  specify, which subsets are boundary
    for(size_t s = 0; s < bndSSGrp.size(); ++s)
    {
    //  get subset index
      const int bndSubset = bndSSGrp[s];
 
    //  request this subset index as boundary subset. This will force the
    //  creation of boundary subsets when calling geo.update
      geo.add_boundary_subset(bndSubset);
    }
 
  //  vector of corner coordinates of element corners (to be filled for each elem)
    std::vector<MathVector<dim> > vCorner;
 
  //  loop elements of subset
    for( ; iter != iterEnd; ++iter)
    {
    //  get element
      grid_base_object* elem = *iter;
 
    //  get all corner coordinates
      CollectCornerCoordinates(vCorner, *elem, u.domain()->position_accessor(), true);
 
    //  compute bf and grads at bip for element
      try{
        geo.update(elem, &vCorner[0], u.domain()->subset_handler().get());
      }
      UG_CATCH_THROW("IntegrateNormalGradientOnManifold: "
            "Cannot update Finite Volume Geometry.");
 
    //  get fct multi-indeces of element
      std::vector<DoFIndex> ind;
      u.dof_indices(elem, fct, ind);
 
    //  specify, which subsets are boundary
      for(size_t s = 0; s < bndSSGrp.size(); ++s)
      {
      //  get subset index
        const int bndSubset = bndSSGrp[s];
 
      //  get all bf of this subset
        typedef typename DimFV1Geometry<dim>::BF BF;
        const std::vector<BF>& vBF = geo.bf(bndSubset);
 
      //  loop boundary faces
        for(size_t b = 0; b < vBF.size(); ++b)
        {
        //  get bf
          const BF& bf = vBF[b];
 
        //  get normal on bf
          const MathVector<dim>& normal = bf.normal();
 
        //  check multi indices
          UG_ASSERT(ind.size() == bf.num_sh(),
                    "IntegrateNormalGradientOnManifold::values: Wrong number of"
                " multi indices, ind: "<<ind.size() << ", bf.num_sh: "
                << bf.num_sh());
 
        //  compute gradient of solution at bip
          MathVector<dim> grad; VecSet(grad, 0.0);
          for(size_t sh = 0; sh < bf.num_sh(); ++sh)
          {
            const number fctVal = DoFRef(u, ind[sh]);
 
            VecScaleAdd(grad, 1.0, grad, fctVal, bf.global_grad(sh));
          }
 
        //  sum up contributions
          value -= VecDot(grad, normal);
        }
      }
    }
  }
 
#ifdef UG_PARALLEL
  // sum over processes
  if(pcl::NumProcs() > 1)
  {
    pcl::ProcessCommunicator com;
    number local = value;
    com.allreduce(&local, &value, 1, PCL_DT_DOUBLE, PCL_RO_SUM);
  }
#endif
 
//  return the result
  return value;
}
 
} // namespace ug
 
#endif /*__H__UG__LIB_DISC__FUNCTION_SPACES__INTEGRATE__*/