cluster_element_stacks.h

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/*
 * Copyright (c) 2015:  G-CSC, Goethe University Frankfurt
 * Author: Sebastian Reiter
 * 
 * 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 §7):
 * 
 * (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_cluster_element_stacks
#define __H__UG_cluster_element_stacks
 
#include <stack>
#include "../partitioner.h"
#include "lib_grid/iterators/lg_for_each.h"
#include "lib_grid/algorithms/normal_calculation.h"
 
namespace ug{
 
template <class elem_t, class vector_t>
class ClusterElementStacks : public IPartitionPostProcessor
{
  public:
    ClusterElementStacks()
    {
      VecSet(m_stackingDir, 0);
    }
 
    ClusterElementStacks(
        const Attachment<vector_t>& aPos,
        const vector_t& stackingDir) :
      m_aPos(aPos),
      m_stackingDir(stackingDir)
    {}
 
    virtual ~ClusterElementStacks()
    {}
 
    void set_position_attachment(const Attachment<vector_t>& aPos)
    {
      m_aPos = aPos;
    }
 
    void set_stacking_direction(const vector_t& stackingDir)
    {
      m_stackingDir = stackingDir;
    }
 
    void init_post_processing(MultiGrid* mg, SubsetHandler* partitions)
    {
      m_mg = mg;
      m_partitions = partitions;
      mg->attach_to<elem_t>(m_aProcessed);
    }
 
    void post_process(int partitionLvl)
    {
      using namespace std;
 
      UG_COND_THROW(VecLengthSq(m_stackingDir) == 0,
              "Please specify a valid stacking direction. "
              "Current stacking direction has length 0.");
      UG_COND_THROW(!m_mg, "no valid grid was specified during 'init_post_processing'");
      UG_COND_THROW(!m_partitions, "no valid partition map was specified during "
              "'init_post_processing'");
      UG_COND_THROW(!m_mg->has_vertex_attachment(m_aPos), "Please specify "
              "a valid position attachment (attached to the underlying grid) "
              "before performing partitioning through "
              "'ClusterElementStacks::set_position_attachment'.");
 
      MultiGrid& mg = *m_mg;
      SubsetHandler& sh = *m_partitions;
 
      Grid::VertexAttachmentAccessor<Attachment<vector_t> > aaPos(mg, m_aPos);
      Grid::AttachmentAccessor<elem_t, ABool> aaProcessed(mg, m_aProcessed);
 
    //  set all processed flags to false in this level
      SetAttachmentValues(aaProcessed, mg.begin<elem_t>(partitionLvl),
                mg.end<elem_t>(partitionLvl), false);
 
      vector_t stackingDir;
      VecNormalize(stackingDir, m_stackingDir);
 
    //  iterate over all elements. If one was already processed, ignore it.
    //  For each unprocessed element: Init the current stack with this element.
    //  Then traverse all elements which are neighbored to a stack element
    //  and which are connected by a side which is not orthogonal to the
    //  stacking direction. Add those elements to the stack.
    
      stack<elem_t*>  stack;
      typename Grid::traits<elem_t>::secure_container elems;
      typename Grid::traits<side_t>::secure_container sides;
 
      lg_for_each_in_lvl_template(elem_t, rootElem, mg, partitionLvl){
        if(aaProcessed[rootElem])
          continue;
 
        int newSi = sh.get_subset_index(rootElem);
        
        stack.push(rootElem);
        aaProcessed[rootElem] = true;
 
        while(!stack.empty()){
          elem_t* elem = stack.top();
          stack.pop();
 
          mg.associated_elements(sides, elem);
          for_each_in_vec(side_t* s, sides){
            vector_t n = CalculateNormal(s, aaPos);
            if(fabs(VecDot(n, stackingDir)) > SMALL){
            //  cluster neighbors of that side
              mg.associated_elements(elems, s);
              for_each_in_vec(elem_t* nbr, elems){
                if(!aaProcessed[nbr]){
                  stack.push(nbr);
                  aaProcessed[nbr] = true;
                  sh.assign_subset(nbr, newSi);
                } 
              }end_for;
            }
          }end_for;
        }
      }lg_end_for;
    }
 
    void partitioning_done()
    {
      m_mg->detach_from<elem_t>(m_aProcessed);
    }
 
  private:
    typedef typename elem_t::side   side_t;
    typedef Attachment<vector_t>    a_position_t;
 
    MultiGrid*    m_mg;
    SubsetHandler*  m_partitions;
    ABool     m_aProcessed;
    a_position_t  m_aPos;
    vector_t    m_stackingDir;
};
 
 
}// end of namespace
 
#endif  //__H__UG_cluster_element_stacks