MeshDistributor.cc

//
// Software License for AMDiS
//
// Copyright (c) 2010 Dresden University of Technology 
// All rights reserved.
// Authors: Simon Vey, Thomas Witkowski et al.
//
// This file is part of AMDiS
//
// See also license.opensource.txt in the distribution.


#include <algorithm>
#include <iostream>
#include <fstream>
#include <limits>
#include <stdint.h>
#include <boost/lexical_cast.hpp>
#include <boost/filesystem.hpp>

#include "parallel/MeshDistributor.h"
#include "parallel/MeshManipulation.h"
#include "parallel/ParallelDebug.h"
#include "parallel/StdMpi.h"
#include "parallel/ParMetisPartitioner.h"
#include "io/ElementFileWriter.h"
#include "io/MacroInfo.h"
#include "io/VtkWriter.h"
#include "Mesh.h"
#include "Traverse.h"
#include "ElInfo.h"
#include "Element.h"
#include "MacroElement.h"
#include "DOFMatrix.h"
#include "DOFVector.h"
#include "SystemVector.h"
#include "ElementDofIterator.h"
#include "ProblemStatBase.h"
#include "StandardProblemIteration.h"
#include "VertexVector.h"
#include "MeshStructure.h"
#include "ProblemVec.h"
#include "ProblemInstat.h"
#include "Debug.h"

namespace AMDiS {

  using boost::lexical_cast;
  using namespace boost::filesystem;

  inline bool cmpDofsByValue(const DegreeOfFreedom* dof1, const DegreeOfFreedom* dof2)
  {
    return (*dof1 < *dof2);
  }


  MeshDistributor::MeshDistributor(std::string str)
    : probStat(0),
      name(str),
      feSpace(NULL),
      mesh(NULL),
      refineManager(NULL),
      info(10),
      partitioner(NULL),
      nRankDofs(0),
      nOverallDofs(0),
      rstart(0),
      deserialized(false),
      writeSerializationFile(false),
      repartitioningAllowed(false),
      repartitionIthChange(20),
      nTimestepsAfterLastRepartitioning(0),
      repartCounter(0),
      debugOutputDir(""),
      lastMeshChangeIndex(0)
  {
    FUNCNAME("MeshDistributor::ParalleDomainBase()");

    mpiRank = MPI::COMM_WORLD.Get_rank();
    mpiSize = MPI::COMM_WORLD.Get_size();
    mpiComm = MPI::COMM_WORLD;

    int tmp = 0;
    GET_PARAMETER(0, name + "->repartitioning", "%d", &tmp);
    repartitioningAllowed = (tmp > 0);

    GET_PARAMETER(0, name + "->debug output dir", &debugOutputDir);
    GET_PARAMETER(0, name + "->repartition ith change", "%d", &repartitionIthChange);

    tmp = 0;
    GET_PARAMETER(0, name + "->log main rank", "%d", &tmp);
    Msg::outputMainRank = (tmp > 0);
  }


  void MeshDistributor::initParallelization()
  {
    FUNCNAME("MeshDistributor::initParallelization()");

    TEST_EXIT(mpiSize > 1)
      ("Parallelization does not work with only one process!\n");

    TEST_EXIT(feSpace)("No FE space has been defined for the mesh distributor!\n");
    TEST_EXIT(mesh)("No mesh has been defined for the mesh distributor!\n");

    // If the problem has been already read from a file, we need only to set
    // isRankDofs to all matrices and rhs vector and to remove periodic 
    // boundary conditions (if there are some).
    if (deserialized) {
      updateMacroElementInfo();

      setRankDofs();

      removePeriodicBoundaryConditions();

      macroElIndexMap.clear();
      macroElIndexTypeMap.clear();

      std::map<int, bool>& elementInRank = partitioner->getElementInRank();
      for (std::vector<MacroElement*>::iterator it = allMacroElements.begin();
	   it != allMacroElements.end(); ++it) {
	elementInRank[(*it)->getIndex()] = false;
	macroElIndexMap[(*it)->getIndex()] = (*it)->getElement();
	macroElIndexTypeMap[(*it)->getIndex()] = (*it)->getElType();
      }

      for (std::deque<MacroElement*>::iterator it = mesh->getMacroElements().begin();
	   it != mesh->getMacroElements().end(); ++it)
	elementInRank[(*it)->getIndex()] = true;      

      return;
    }

   
    // Test, if the mesh is the macro mesh only! Paritioning of the mesh is supported
    // only for macro meshes, so it will not work yet if the mesh is already refined
    // in some way.
    testForMacroMesh();

    // For later mesh repartitioning, we need to store some information about the
    // macro mesh.
    createMacroElementInfo();

    // create an initial partitioning of the mesh
    partitioner->createPartitionData();

    // set the element weights, which are 1 at the very first begin
    setInitialElementWeights();

    // and now partition the mesh    
    partitioner->fillCoarsePartitionVec(&oldPartitionVec);

    bool partitioningSucceed = partitioner->partition(elemWeights, INITIAL);
    TEST_EXIT(partitioningSucceed)("Initial partitioning does not work!\n");

    partitioner->fillCoarsePartitionVec(&partitionVec);


#if (DEBUG != 0)
    debug::ElementIdxToDofs elMap;
    debug::createSortedDofs(mesh, elMap);
    if (mpiRank == 0) {
      int writePartMesh = 1;
      GET_PARAMETER(0, "dbg->write part mesh", "%d", &writePartMesh);

      if (writePartMesh > 0) {
	debug::writeElementIndexMesh(mesh, debugOutputDir + "elementIndex.vtu");
	writePartitioningMesh(debugOutputDir + "part.vtu");
      } else {
	MSG("Skip write part mesh!\n");
      }
    }
#endif


    // === Create interior boundary information. ===

    createInteriorBoundaryInfo();

#if (DEBUG != 0)
    ParallelDebug::printBoundaryInfo(*this);
#endif


    // === Remove all macro elements that are not part of the rank partition. ===

    removeMacroElements();


    // === Create new global and local DOF numbering. ===


    // We have to remove the VertexVectors, which contain periodic assoiciations, 
    // because they are not valid anymore after some macro elements have been removed
    // and the corresponding DOFs were deleted.
    for (std::map<BoundaryType, VertexVector*>::iterator it = mesh->getPeriodicAssociations().begin();
	 it != mesh->getPeriodicAssociations().end(); ++it)
      const_cast<DOFAdmin&>(mesh->getDofAdmin(0)).removeDOFContainer(dynamic_cast<DOFContainer*>(it->second));

    updateLocalGlobalNumbering();


    // === If in debug mode, make some tests. ===

#if (DEBUG != 0)
    MSG("AMDiS runs in debug mode, so make some test ...\n");

    ParallelDebug::testAllElements(*this);
    debug::testSortedDofs(mesh, elMap);
    ParallelDebug::testInteriorBoundary(*this);
    ParallelDebug::testCommonDofs(*this, true);
    ParallelDebug::testGlobalIndexByCoords(*this);

    debug::writeMesh(feSpace, -1, debugOutputDir + "macro_mesh");   

    MSG("Debug mode tests finished!\n");
#endif


    // === Create periodic dof mapping, if there are periodic boundaries. ===

    createPeriodicMap();    


    // === Global refinements. ===

    int globalRefinement = 0;
    GET_PARAMETER(0, mesh->getName() + "->global refinements", "%d", &globalRefinement);

    if (globalRefinement > 0) {
      refineManager->globalRefine(mesh, globalRefinement);

      updateLocalGlobalNumbering();

     
      // === Update periodic mapping, if there are periodic boundaries. ===     

      createPeriodicMap();
    }


    /// === Set DOF rank information to all matrices and vectors. ===

    setRankDofs();


    // === Remove periodic boundary conditions in sequential problem definition. ===

    removePeriodicBoundaryConditions();
  }


  void MeshDistributor::addProblemStat(ProblemVec *probVec)
  {
    FUNCNAME("MeshDistributor::addProblemVec()");

    if (feSpace != NULL) {
      std::vector<FiniteElemSpace*> feSpaces = probVec->getFeSpaces();
      for (unsigned int i = 0; i < feSpaces.size(); i++) {
	TEST_EXIT(feSpace == feSpaces[i])
	  ("Parallelizaton is not supported for multiple FE spaces!\n");
      }
    } else {
      feSpace = probVec->getFeSpace(0);
      mesh = feSpace->getMesh();
      info = probVec->getInfo();
      
      TEST_EXIT(mesh->getNumberOfDOFAdmin() == 1)
	("Only meshes with one DOFAdmin are supported!\n");
      TEST_EXIT(mesh->getDofAdmin(0).getNumberOfPreDofs(VERTEX) == 0)
	("Wrong pre dof number for DOFAdmin!\n");
      
      switch (mesh->getDim()) {
      case 2:
	refineManager = new RefinementManager2d();
	break;
      case 3:
	refineManager = new RefinementManager3d();
	break;
      default:
	ERROR_EXIT("This should not happen for dim = %d!\n", mesh->getDim());
      }

      partitioner = new ParMetisPartitioner(mesh, &mpiComm);
    }

    // Create parallel serialization file writer, if needed.
    int writeSerialization = 0;
    GET_PARAMETER(0, probVec->getName() + "->output->write serialization", "%d", 
		  &writeSerialization);
    if (writeSerialization && !writeSerializationFile) {
      std::string filename = "";
      GET_PARAMETER(0, name + "->output->serialization filename", &filename);
      
      TEST_EXIT(filename != "")
	("No filename defined for parallel serialization file!\n");

      int tsModulo = -1;
      GET_PARAMETER(0, probVec->getName() + "->output->write every i-th timestep", 
		    "%d", &tsModulo);
      
      probVec->getFileWriterList().push_back(new Serializer<MeshDistributor>(this, filename, tsModulo));
      writeSerializationFile = true;
    }    

    int readSerialization = 0;
    GET_PARAMETER(0, probVec->getName() + "->input->read serialization", "%d", 
		  &readSerialization);
    if (readSerialization) {
      std::string filename = "";
      GET_PARAMETER(0, probVec->getName() + "->input->serialization filename", &filename);
      filename += ".p" + lexical_cast<std::string>(mpiRank);
      MSG("Start deserialization with %s\n", filename.c_str());
      std::ifstream in(filename.c_str());

      TEST_EXIT(!in.fail())("Could not open deserialization file: %s\n",
			    filename.c_str());

      probVec->deserialize(in);
      in.close();
      MSG("Deserialization from file: %s\n", filename.c_str());

      filename = "";
      GET_PARAMETER(0, name + "->input->serialization filename", &filename);
      
      TEST_EXIT(filename != "")
	("No filename defined for parallel deserialization file!\n");
      
      std::string rankFilename = filename + ".p" + lexical_cast<std::string>(mpiRank);
      in.open(rankFilename.c_str());
      
      TEST_EXIT(!in.fail())("Could not open parallel deserialization file: %s\n",
			    filename.c_str());
      
      deserialize(in);
      in.close();
      MSG("Deserializtion of mesh distributor from file: %s\n", rankFilename.c_str());
      deserialized = true;
    }

    probStat.push_back(probVec);
  }


  void MeshDistributor::exitParallelization()
  {}

  
  void MeshDistributor::testForMacroMesh()
  {
    FUNCNAME("MeshDistributor::testForMacroMesh()");

    int nMacroElements = 0;

    TraverseStack stack;
    ElInfo *elInfo = stack.traverseFirst(mesh, -1, Mesh::CALL_LEAF_EL);
    while (elInfo) {
      TEST_EXIT(elInfo->getLevel() == 0)
	("Mesh is already refined! This does not work with parallelization!\n");

      TEST_EXIT(elInfo->getType() == 0)
	("Only macro elements with level 0 are supported!\n");
      
      nMacroElements++;

      elInfo = stack.traverseNext(elInfo);
    }

    TEST_EXIT(nMacroElements >= mpiSize)
      ("The mesh has less macro elements than number of mpi processes!\n");
  }


  void MeshDistributor::synchVector(DOFVector<double> &vec)
  {
    StdMpi<std::vector<double> > stdMpi(mpiComm);

    for (RankToDofContainer::iterator sendIt = sendDofs.begin();
	 sendIt != sendDofs.end(); ++sendIt) {
      std::vector<double> dofs;
      int nSendDofs = sendIt->second.size();
      dofs.reserve(nSendDofs);
      
      for (int i = 0; i < nSendDofs; i++)
	dofs.push_back(vec[*((sendIt->second)[i])]);

      stdMpi.send(sendIt->first, dofs);
    }

    for (RankToDofContainer::iterator recvIt = recvDofs.begin();
	 recvIt != recvDofs.end(); ++recvIt)
      stdMpi.recv(recvIt->first, recvIt->second.size());

    stdMpi.startCommunication<double>(MPI_DOUBLE);

    for (RankToDofContainer::iterator recvIt = recvDofs.begin();
	 recvIt != recvDofs.end(); ++recvIt)
      for (unsigned int i = 0; i < recvIt->second.size(); i++)
	vec[*(recvIt->second)[i]] = stdMpi.getRecvData(recvIt->first)[i];
  }


  void MeshDistributor::synchVector(SystemVector &vec)
  {
    int nComponents = vec.getSize();
    StdMpi<std::vector<double> > stdMpi(mpiComm);

    for (RankToDofContainer::iterator sendIt = sendDofs.begin();
	 sendIt != sendDofs.end(); ++sendIt) {
      std::vector<double> dofs;
      int nSendDofs = sendIt->second.size();
      dofs.reserve(nComponents * nSendDofs);
      
      for (int i = 0; i < nComponents; i++) {
	DOFVector<double> *dofvec = vec.getDOFVector(i);
	for (int j = 0; j < nSendDofs; j++)
	  dofs.push_back((*dofvec)[*((sendIt->second)[j])]);
      }

      stdMpi.send(sendIt->first, dofs);
    }

    for (RankToDofContainer::iterator recvIt = recvDofs.begin();
	 recvIt != recvDofs.end(); ++recvIt)
      stdMpi.recv(recvIt->first, recvIt->second.size() * nComponents);

    stdMpi.startCommunication<double>(MPI_DOUBLE);

    for (RankToDofContainer::iterator recvIt = recvDofs.begin();
	 recvIt != recvDofs.end(); ++recvIt) {
      int nRecvDofs = recvIt->second.size();

      int counter = 0;
      for (int i = 0; i < nComponents; i++) {
	DOFVector<double> *dofvec = vec.getDOFVector(i);
 	for (int j = 0; j < nRecvDofs; j++)
	  (*dofvec)[*(recvIt->second)[j]] = 
	    stdMpi.getRecvData(recvIt->first)[counter++];
      }
    }
  }


  void MeshDistributor::setRankDofs()
  {
    for (unsigned int i = 0; i < probStat.size(); i++) {
      int nComponents = probStat[i]->getNumComponents();
      for (int j = 0; j < nComponents; j++) {
	for (int k = 0; k < nComponents; k++)
	  if (probStat[i]->getSystemMatrix(j, k))
	    probStat[i]->getSystemMatrix(j, k)->setRankDofs(isRankDof);

	TEST_EXIT_DBG(probStat[i]->getRhs()->getDOFVector(j))("No RHS vector!\n");
	TEST_EXIT_DBG(probStat[i]->getSolution()->getDOFVector(j))("No solution vector!\n");
	
	probStat[i]->getRhs()->getDOFVector(j)->setRankDofs(isRankDof);
	probStat[i]->getSolution()->getDOFVector(j)->setRankDofs(isRankDof);
      }
    }
  }


  void MeshDistributor::removePeriodicBoundaryConditions()
  {
    FUNCNAME("MeshDistributor::removePeriodicBoundaryConditions()");

    // Remove periodic boundaries in boundary manager on matrices and vectors.
    for (unsigned int i = 0; i < probStat.size(); i++) {
      int nComponents = probStat[i]->getNumComponents();

      for (int j = 0; j < nComponents; j++) {
	for (int k = 0; k < nComponents; k++) {
	  DOFMatrix* mat = probStat[i]->getSystemMatrix(j, k);
	  if (mat && mat->getBoundaryManager())
	    removePeriodicBoundaryConditions(const_cast<BoundaryIndexMap&>(mat->getBoundaryManager()->getBoundaryConditionMap()));
	}
	
	if (probStat[i]->getSolution()->getDOFVector(j)->getBoundaryManager())
	  removePeriodicBoundaryConditions(const_cast<BoundaryIndexMap&>(probStat[i]->getSolution()->getDOFVector(j)->getBoundaryManager()->getBoundaryConditionMap()));
	
	if (probStat[i]->getRhs()->getDOFVector(j)->getBoundaryManager())
	  removePeriodicBoundaryConditions(const_cast<BoundaryIndexMap&>(probStat[i]->getRhs()->getDOFVector(j)->getBoundaryManager()->getBoundaryConditionMap()));
      }
    }

    // Remove periodic boundaries on elements in mesh.
    TraverseStack stack;
    ElInfo *elInfo = stack.traverseFirst(mesh,  -1, Mesh::CALL_EVERY_EL_PREORDER);
    while (elInfo) {
      elInfo->getElement()->deleteElementData(PERIODIC);
      elInfo = stack.traverseNext(elInfo);
    }    

    // Remove periodic vertex associations
    mesh->getPeriodicAssociations().clear();
  }


  void MeshDistributor::removePeriodicBoundaryConditions(BoundaryIndexMap& boundaryMap)
  {
    BoundaryIndexMap::iterator it = boundaryMap.begin();
    while (it != boundaryMap.end()) {
      if (it->second->isPeriodic())
	boundaryMap.erase(it++);
      else
	++it;      
    }    
  }


  void MeshDistributor::checkMeshChange()
  {
    FUNCNAME("MeshDistributor::checkMeshChange()");    

#if (DEBUG != 0)
    debug::writeMesh(feSpace, -1, debugOutputDir + "before_check_mesh");
#endif

    double first = MPI::Wtime();

    // === If mesh has not been changed on all ranks, return. ===

    int recvAllValues = 0;
    int sendValue = static_cast<int>(mesh->getChangeIndex() != lastMeshChangeIndex);
    mpiComm.Allreduce(&sendValue, &recvAllValues, 1, MPI_INT, MPI_SUM);

    if (recvAllValues == 0)
      return;

    // === At least one rank mesh has been changed, so the boundaries must be ===
    // === adapted to the new mesh structure.                                 ===
   
    do {
      // To check the interior boundaries, the ownership of the boundaries is not 
      // important. Therefore, we add all boundaries to one boundary container.
      RankToBoundMap allBound;

      for (InteriorBoundary::iterator it(myIntBoundary); !it.end(); ++it)
	if ((mesh->getDim() == 2 && it->rankObj.subObj == EDGE) || 
	    (mesh->getDim() == 3 && it->rankObj.subObj == FACE))
 	  allBound[it.getRank()].push_back(*it);

      for (InteriorBoundary::iterator it(otherIntBoundary); !it.end(); ++it)
	if ((mesh->getDim() == 2 && it->rankObj.subObj == EDGE) || 
	    (mesh->getDim() == 3 && it->rankObj.subObj == FACE))
	  allBound[it.getRank()].push_back(*it);

      for (InteriorBoundary::iterator it(periodicBoundary); !it.end(); ++it) {
	if (it.getRank() == mpiRank) {
	  //	  ERROR_EXIT("Na, du weisst schon!\n");
	} else {
	  if ((mesh->getDim() == 2 && it->rankObj.subObj == EDGE) || 
	      (mesh->getDim() == 3 && it->rankObj.subObj == FACE))
	    allBound[it.getRank()].push_back(*it);	
	}
      }


      // === Check the boundaries and adapt mesh if necessary. ===
#if (DEBUG != 0)
      MSG("Run checkAndAdaptBoundary ...\n");
#endif

      bool meshChanged = checkAndAdaptBoundary(allBound);

      // === Check on all ranks if at least one rank's mesh has changed. ===

      int sendValue = static_cast<int>(!meshChanged);
      recvAllValues = 0;
      mpiComm.Allreduce(&sendValue, &recvAllValues, 1, MPI_INT, MPI_SUM);

#if (DEBUG != 0)
      MSG("Mesh changed on %d ranks!\n", recvAllValues);
#endif
    } while (recvAllValues != 0);

#if (DEBUG != 0)
    debug::writeMesh(feSpace, -1, debugOutputDir + "mesh");
#endif

    // === Because the mesh has been changed, update the DOF numbering and mappings. ===

    updateLocalGlobalNumbering();


    // === Update periodic mapping, if there are periodic boundaries. ===

    createPeriodicMap();    


    INFO(info, 8)("Parallel mesh adaption needed %.5f seconds\n", 
		  MPI::Wtime() - first);


    // === The mesh has changed, so check if it is required to repartition the mesh. ===

    nTimestepsAfterLastRepartitioning++;

    if (repartitioningAllowed) {
      if (nTimestepsAfterLastRepartitioning >= repartitionIthChange) {
	repartitionMesh();
	nTimestepsAfterLastRepartitioning = 0;
      }
    }
  }

  
  bool MeshDistributor::checkAndAdaptBoundary(RankToBoundMap &allBound)
  {
    FUNCNAME("MeshDistributor::checkAndAdaptBoundary()");

    // === Create mesh structure codes for all ranks boundary elements. ===
       
    std::map<int, MeshCodeVec> sendCodes;
   
    for (RankToBoundMap::iterator it = allBound.begin(); it != allBound.end(); ++it) {

      for (std::vector<AtomicBoundary>::iterator boundIt = it->second.begin();
	   boundIt != it->second.end(); ++boundIt) {
	MeshStructure elCode;
	elCode.init(boundIt->rankObj);
	sendCodes[it->first].push_back(elCode);
      }
    }

    StdMpi<MeshCodeVec> stdMpi(mpiComm, true);
    stdMpi.send(sendCodes);
    stdMpi.recv(allBound);
    stdMpi.startCommunication<uint64_t>(MPI_UNSIGNED_LONG);
 
    // === Compare received mesh structure codes. ===
    
    bool meshFitTogether = true;

    for (RankToBoundMap::iterator it = allBound.begin(); it != allBound.end(); ++it) {
     
      MeshCodeVec &recvCodes = stdMpi.getRecvData()[it->first];
      int i = 0;
      
      for (std::vector<AtomicBoundary>::iterator boundIt = it->second.begin();
	   boundIt != it->second.end(); ++boundIt) {

	MeshStructure elCode;	
	elCode.init(boundIt->rankObj);

	if (elCode.getCode() != recvCodes[i].getCode()) {
	  TEST_EXIT_DBG(refineManager)("Refinement manager is not set correctly!\n");

	  bool b = startFitElementToMeshCode(recvCodes[i], 
					     boundIt->rankObj.el,
					     boundIt->rankObj.subObj,
					     boundIt->rankObj.ithObj, 
					     boundIt->rankObj.elType,
					     boundIt->rankObj.reverseMode);

	  if (b)
	    meshFitTogether = false;	  
 	}

	i++;
      }
    }

    return meshFitTogether;
  }


  bool MeshDistributor::startFitElementToMeshCode(MeshStructure &code, 
						  Element *el, 
						  GeoIndex subObj,
						  int ithObj, 
						  int elType,
						  bool reverseMode)
  {
    FUNCNAME("MeshDistributor::startFitElementToMeshCode()");

    TEST_EXIT_DBG(el)("No element given!\n");

    // If the code is empty, the element does not matter and the function can
    // return without chaning the mesh.
    if (code.empty())
      return false;

    // s0 and s1 are the number of the edge/face in both child of the element,
    // which contain the edge/face the function has to traverse through. If the
    // edge/face is not contained in one of the children, s0 or s1 is -1.
    int s0 = el->getSubObjOfChild(0, subObj, ithObj, elType);
    int s1 = el->getSubObjOfChild(1, subObj, ithObj, elType);

    TEST_EXIT_DBG(s0 != -1 || s1 != -1)("This should not happen!\n");

    bool meshChanged = false;
    Flag traverseFlag = 
      Mesh::CALL_EVERY_EL_PREORDER | Mesh::FILL_NEIGH | Mesh::FILL_BOUND;

    // Test for reverse mode, in which the left and right children of elements
    // are flipped.
    if (reverseMode)
      traverseFlag |= Mesh::CALL_REVERSE_MODE;    


    // === If the edge/face is contained in both children. ===

    if (s0 != -1 && s1 != -1) {
      // Create traverse stack and traverse within the mesh until the element,
      // which should be fitted to the mesh structure code, is reached.
      TraverseStack stack;
      ElInfo *elInfo = stack.traverseFirst(el->getMesh(), -1, traverseFlag);
      while (elInfo && elInfo->getElement() != el)
	elInfo = stack.traverseNext(elInfo);      

      TEST_EXIT_DBG(elInfo->getElement() == el)("This should not happen!\n");

      meshChanged = fitElementToMeshCode(code, stack, subObj, ithObj, reverseMode);
      return meshChanged;
    }


    // === The edge/face is contained in only on of the both children. ===

    if (el->isLeaf()) {

      // If element is leaf and code contains only one leaf element, we are finished.
      if (code.getNumElements() == 1 && code.isLeafElement())
	return false;     

      // Create traverse stack and traverse the mesh to the element.
      TraverseStack stack;
      ElInfo *elInfo = stack.traverseFirst(el->getMesh(), -1, traverseFlag);
      while (elInfo && elInfo->getElement() != el)
	elInfo = stack.traverseNext(elInfo);      

      TEST_EXIT_DBG(elInfo)("This should not happen!\n");

      // Code is not leaf, therefore refine the element.
      el->setMark(1);
      refineManager->setMesh(el->getMesh());
      refineManager->setStack(&stack);
      refineManager->refineFunction(elInfo);
      meshChanged = true;
    }

    Element *child0 = el->getFirstChild();
    Element *child1 = el->getSecondChild();
    if (reverseMode) {
      std::swap(s0, s1);
      std::swap(child0, child1);    
    }

    // === We know that the edge/face is contained in only one of the children. ===
    // === Therefore, traverse the mesh to this children and fit this element   ===
    // === To the mesh structure code.                                          ===

    TraverseStack stack;
    ElInfo *elInfo = stack.traverseFirst(el->getMesh(), -1, traverseFlag);

    if (s0 != -1) {
      while (elInfo && elInfo->getElement() != child0)
	elInfo = stack.traverseNext(elInfo);     

      meshChanged |= fitElementToMeshCode(code, stack, subObj, s0, reverseMode);
    } else {
      while (elInfo && elInfo->getElement() != child1) 
	elInfo = stack.traverseNext(elInfo);      

      meshChanged |= fitElementToMeshCode(code, stack, subObj, s1, reverseMode);
    }


    return meshChanged;
  }


  bool MeshDistributor::fitElementToMeshCode(MeshStructure &code, 
					     TraverseStack &stack,
					     GeoIndex subObj,
					     int ithObj, 
					     bool reverseMode)
  {
    FUNCNAME("MeshDistributor::fitElementToMeshCode()");


    // === Test if there are more elements in stack to check with the code. ===

    ElInfo *elInfo = stack.getElInfo();
    if (!elInfo)
      return false;


    // === Test if code contains a leaf element. If this is the case, the ===
    // === current element is finished. Traverse the mesh to the next     ===
    // === coarser element.                                               ===

    if (code.isLeafElement()) {
      int level = elInfo->getLevel();

      do {
	elInfo = stack.traverseNext(elInfo);
      } while (elInfo && elInfo->getLevel() > level);

      return false;
    }


    bool meshChanged = false;
    Element *el = elInfo->getElement();


    // === If element is leaf (and the code is not), refine the element. ===

    if (el->isLeaf()) {
      TEST_EXIT_DBG(elInfo->getLevel() < 255)("This should not happen!\n");

      el->setMark(1);
      refineManager->setMesh(el->getMesh());
      refineManager->setStack(&stack);
      refineManager->refineFunction(elInfo);
      meshChanged = true;
    }


    // === Continue fitting the mesh structure code to the children of the ===
    // === current element.                                                ===

    int s0 = el->getSubObjOfChild(0, subObj, ithObj, elInfo->getType());
    int s1 = el->getSubObjOfChild(1, subObj, ithObj, elInfo->getType());
    Element *child0 = el->getFirstChild();
    Element *child1 = el->getSecondChild();
    if (reverseMode) {
      std::swap(s0, s1);
      std::swap(child0, child1);
    }

    
    // === Traverse left child. ===

    if (s0 != -1) {
      // The edge/face is contained in the left child, therefore fit this
      // child to the mesh structure code.

      stack.traverseNext(elInfo);
      code.nextElement();
      meshChanged |= fitElementToMeshCode(code, stack, subObj, s0, reverseMode);
      elInfo = stack.getElInfo();
    } else {
      // The edge/face is not contained in the left child. Hence we need
      // to traverse through all subelements of the left child until we get
      // the second child of the current element.

      do {
	elInfo = stack.traverseNext(elInfo);
      } while (elInfo && elInfo->getElement() != child1); 

      TEST_EXIT_DBG(elInfo != NULL)("This should not happen!\n");
    }  

    TEST_EXIT_DBG(elInfo->getElement() == child1)
      ("Got wrong child with idx = %d! Searched for child idx = %d\n",
       elInfo->getElement()->getIndex(), child1->getIndex());


    // === Traverse right child. ===

    if (s1 != -1) {
      // The edge/face is contained in the right child, therefore fit this
      // child to the mesh structure code.

      code.nextElement();
      meshChanged |= fitElementToMeshCode(code, stack, subObj, s1, reverseMode);
    } else {
      // The edge/face is not contained in the right child. Hence we need
      // to traverse through all subelements of the right child until we have
      // finished traversing the current element with all its subelements.

      int level = elInfo->getLevel();

      do {
	elInfo = stack.traverseNext(elInfo);
      } while (elInfo && elInfo->getLevel() > level);
    }


    return meshChanged;
  }

  
  void MeshDistributor::serialize(std::ostream &out, DofContainer &data)
  {    
    int vecSize = data.size();
    SerUtil::serialize(out, vecSize);
    for (int i = 0; i < vecSize; i++) {
      int dofIndex = *(data[i]);
      SerUtil::serialize(out, dofIndex);
    }
  }


  void MeshDistributor::deserialize(std::istream &in, DofContainer &data,
				    std::map<int, const DegreeOfFreedom*> &dofMap)
  {
    FUNCNAME("MeshDistributor::deserialize()");

    int vecSize = 0;
    SerUtil::deserialize(in, vecSize);
    data.clear();
    data.resize(vecSize);
    for (int i = 0; i < vecSize; i++) {
      int dofIndex = 0;
      SerUtil::deserialize(in, dofIndex);

      TEST_EXIT_DBG(dofMap.count(dofIndex) != 0)
	("Dof index could not be deserialized correctly!\n");

      data[i] = dofMap[dofIndex];
    }
  }