Exemplo n.º 1
0
  void AlgebraicPermutationStrategy<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps>::BuildPermutation(const Teuchos::RCP<Matrix> & A, const Teuchos::RCP<const Map> permRowMap, Level & currentLevel, const FactoryBase* genFactory) const {
#ifndef HAVE_MUELU_INST_COMPLEX_INT_INT

  const Teuchos::RCP< const Teuchos::Comm< int > > comm = A->getRowMap()->getComm();
  int numProcs = comm->getSize();
  int myRank   = comm->getRank();

  /*if( permRowMap == Teuchos::null ) {
    permRowMap = A->getRowMap(); // use full row map of A
  }*/

  size_t nDofsPerNode = 1;
  if (A->IsView("stridedMaps")) {
    Teuchos::RCP<const Map> permRowMapStrided = A->getRowMap("stridedMaps");
    nDofsPerNode = Teuchos::rcp_dynamic_cast<const StridedMap>(permRowMapStrided)->getFixedBlockSize();
  }

  //GetOStream(Runtime0, 0) << "Perform generation of permutation operators on " << mapName_ << " map with " << permRowMap->getGlobalNumElements() << " elements" << std::endl;

  std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> > permutedDiagCandidates;
  std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> > keepDiagonalEntries;
  std::vector<Scalar> Weights;

  // loop over all local rows in matrix A and keep diagonal entries if corresponding
  // matrix rows are not contained in permRowMap
  for (size_t row = 0; row < A->getRowMap()->getNodeNumElements(); row++) {
    GlobalOrdinal grow = A->getRowMap()->getGlobalElement(row);

    if(permRowMap->isNodeGlobalElement(grow) == true) continue;

    size_t nnz = A->getNumEntriesInLocalRow(row);

    // extract local row information from matrix
    Teuchos::ArrayView<const LocalOrdinal> indices;
    Teuchos::ArrayView<const Scalar> vals;
    A->getLocalRowView(row, indices, vals);

    TEUCHOS_TEST_FOR_EXCEPTION(Teuchos::as<size_t>(indices.size()) != nnz, Exceptions::RuntimeError, "MueLu::PermutationFactory::Build: number of nonzeros not equal to number of indices? Error.");

    // find column entry with max absolute value
    GlobalOrdinal gMaxValIdx = 0;
    Scalar norm1 = 0.0;
    Scalar maxVal = 0.0;
    for (size_t j = 0; j < Teuchos::as<size_t>(indices.size()); j++) {
      norm1 += std::abs(vals[j]);
      if(std::abs(vals[j]) > maxVal) {
        maxVal = std::abs(vals[j]);
        gMaxValIdx = A->getColMap()->getGlobalElement(indices[j]);
      }
    }

    if(grow == gMaxValIdx) // only keep row/col pair if it's diagonal dominant!!!
      keepDiagonalEntries.push_back(std::make_pair(grow,grow));
  }

  //////////
  // handle rows that are marked to be relevant for permutations
  for (size_t row = 0; row < permRowMap->getNodeNumElements(); row++) {
    GlobalOrdinal grow = permRowMap->getGlobalElement(row);
    LocalOrdinal lArow = A->getRowMap()->getLocalElement(grow);
    size_t nnz = A->getNumEntriesInLocalRow(lArow);

    // extract local row information from matrix
    Teuchos::ArrayView<const LocalOrdinal> indices;
    Teuchos::ArrayView<const Scalar> vals;
    A->getLocalRowView(lArow, indices, vals);

    TEUCHOS_TEST_FOR_EXCEPTION(Teuchos::as<size_t>(indices.size()) != nnz, Exceptions::RuntimeError, "MueLu::PermutationFactory::Build: number of nonzeros not equal to number of indices? Error.");

    // find column entry with max absolute value
    GlobalOrdinal gMaxValIdx = 0;
    Scalar norm1 = 0.0;
    Scalar maxVal = 0.0;
    for (size_t j = 0; j < Teuchos::as<size_t>(indices.size()); j++) {
      norm1 += std::abs(vals[j]);
      if(std::abs(vals[j]) > maxVal) {
        maxVal = std::abs(vals[j]);
        gMaxValIdx = A->getColMap()->getGlobalElement(indices[j]);
      }
    }

    if(std::abs(maxVal) > 0.0) { // keep only max Entries \neq 0.0
      permutedDiagCandidates.push_back(std::make_pair(grow,gMaxValIdx));
      Weights.push_back(maxVal/(norm1*Teuchos::as<Scalar>(nnz)));
    } else {
      std::cout << "ATTENTION: row " << grow << " has only zero entries -> singular matrix!" << std::endl;
    }

  }

  // sort Weights in descending order
  std::vector<int> permutation;
  sortingPermutation(Weights,permutation);

  // create new vector with exactly one possible entry for each column

  // each processor which requests the global column id gcid adds 1 to gColVec
  // gColVec will be summed up over all processors and communicated to gDomVec
  // which is based on the non-overlapping domain map of A.

  Teuchos::RCP<Vector> gColVec = VectorFactory::Build(A->getColMap());
  Teuchos::RCP<Vector> gDomVec = VectorFactory::Build(A->getDomainMap());
  gColVec->putScalar(0.0);
  gDomVec->putScalar(0.0);

  // put in all keep diagonal entries
  for (typename std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> >::const_iterator p = keepDiagonalEntries.begin(); p != keepDiagonalEntries.end(); ++p) {
    gColVec->sumIntoGlobalValue((*p).second,1.0);
  }

  Teuchos::RCP<Export> exporter = ExportFactory::Build(gColVec->getMap(), gDomVec->getMap());
  gDomVec->doExport(*gColVec,*exporter,Xpetra::ADD);  // communicate blocked gcolids to all procs
  gColVec->doImport(*gDomVec,*exporter,Xpetra::INSERT);

  std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> > permutedDiagCandidatesFiltered; // TODO reserve memory
  std::map<GlobalOrdinal, Scalar> gColId2Weight;

  Teuchos::ArrayRCP< Scalar > ddata = gColVec->getDataNonConst(0);
  for(size_t i = 0; i < permutedDiagCandidates.size(); ++i) {
    // loop over all candidates
    std::pair<GlobalOrdinal, GlobalOrdinal> pp = permutedDiagCandidates[permutation[i]];
    GlobalOrdinal grow = pp.first;
    GlobalOrdinal gcol = pp.second;

    LocalOrdinal lcol = A->getColMap()->getLocalElement(gcol);
    //Teuchos::ArrayRCP< Scalar > ddata = gColVec->getDataNonConst(0);
    if(ddata[lcol] > 0.0){
      continue; // skip lcol: column already handled by another row
    }

    // mark column as already taken
    ddata[lcol]++;

    permutedDiagCandidatesFiltered.push_back(std::make_pair(grow,gcol));
    gColId2Weight[gcol] = Weights[permutation[i]];
  }

  // communicate how often each column index is requested by the different procs
  gDomVec->doExport(*gColVec,*exporter,Xpetra::ADD);
  gColVec->doImport(*gDomVec,*exporter,Xpetra::INSERT); // probably not needed // TODO check me

  //*****************************************************************************************
  // first communicate ALL global ids of column indices which are requested by more
  // than one proc to all other procs
  // detect which global col indices are requested by more than one proc
  // and store them in the multipleColRequests vector
  std::vector<GlobalOrdinal> multipleColRequests; // store all global column indices from current processor that are also
                                                  // requested by another processor. This is possible, since they are stored
                                                  // in gDomVec which is based on the nonoverlapping domain map. That is, each
                                                  // global col id is handled by exactly one proc.
  std::queue<GlobalOrdinal> unusedColIdx; // unused column indices on current processor

  for(size_t sz = 0; sz<gDomVec->getLocalLength(); ++sz) {
    Teuchos::ArrayRCP< const Scalar > arrDomVec = gDomVec->getData(0);
    if(arrDomVec[sz] > 1.0) {
      multipleColRequests.push_back(gDomVec->getMap()->getGlobalElement(sz));
    } else if(arrDomVec[sz] == 0.0) {
      unusedColIdx.push(gDomVec->getMap()->getGlobalElement(sz));
    }
  }

  // communicate the global number of column indices which are requested by more than one proc
  LocalOrdinal localMultColRequests  = Teuchos::as<LocalOrdinal>(multipleColRequests.size());
  LocalOrdinal globalMultColRequests = 0;

  // sum up all entries in multipleColRequests over all processors
  sumAll(gDomVec->getMap()->getComm(), (LocalOrdinal)localMultColRequests, globalMultColRequests);

  if(globalMultColRequests > 0) {
    // special handling: two processors request the same global column id.
    // decide which processor gets it

    // distribute number of multipleColRequests to all processors
    // each processor stores how many column ids for exchange are handled by the cur proc
    std::vector<GlobalOrdinal> numMyMultColRequests(numProcs,0);
    std::vector<GlobalOrdinal> numGlobalMultColRequests(numProcs,0);
    numMyMultColRequests[myRank] = localMultColRequests;
    Teuchos::reduceAll(*comm,Teuchos::REDUCE_MAX,numProcs,&numMyMultColRequests[0],&numGlobalMultColRequests[0]);

    // communicate multipleColRequests entries to all processors
    int nMyOffset = 0;
    for (int i=0; i<myRank-1; i++)
      nMyOffset += numGlobalMultColRequests[i]; // calculate offset to store the weights on the corresponding place in procOverlappingWeights

    GlobalOrdinal zero=0;
    std::vector<GlobalOrdinal> procMultRequestedColIds(globalMultColRequests,zero);
    std::vector<GlobalOrdinal> global_procMultRequestedColIds(globalMultColRequests,zero);

    // loop over all local column GIDs that are also requested by other procs
    for(size_t i = 0; i < multipleColRequests.size(); i++) {
      procMultRequestedColIds[nMyOffset + i] = multipleColRequests[i]; // all weights are > 0 ?
    }

    // template ordinal, package (double)
    Teuchos::reduceAll(*comm, Teuchos::REDUCE_MAX, Teuchos::as<int>(globalMultColRequests), &procMultRequestedColIds[0], &global_procMultRequestedColIds[0]);

    // loop over global_procOverlappingWeights and eliminate wrong entries...
    for (size_t k = 0; k<global_procMultRequestedColIds.size(); k++) {
      GlobalOrdinal globColId = global_procMultRequestedColIds[k];

      std::vector<Scalar> MyWeightForColId(numProcs,0);
      std::vector<Scalar> GlobalWeightForColId(numProcs,0);

      if(gColVec->getMap()->isNodeGlobalElement(globColId)) {
        MyWeightForColId[myRank] = gColId2Weight[globColId];
      } else {
        MyWeightForColId[myRank] = 0.0;
      }

      Teuchos::reduceAll(*comm, Teuchos::REDUCE_MAX, numProcs, &MyWeightForColId[0], &GlobalWeightForColId[0]);

      if(gColVec->getMap()->isNodeGlobalElement(globColId)) {
        // note: 2 procs could have the same weight for a column index.
        // pick the first one.
        Scalar winnerValue = 0.0;
        int winnerProcRank = 0;
        for (int proc = 0; proc < numProcs; proc++) {
          if(GlobalWeightForColId[proc] > winnerValue) {
            winnerValue = GlobalWeightForColId[proc];
            winnerProcRank = proc;
          }
        }

        // winnerProcRank is the winner for handling globColId.
        // winnerProcRank is unique (even if two procs have the same weight for a column index)

        if(myRank != winnerProcRank) {
          // remove corresponding entry from permutedDiagCandidatesFiltered
          typename std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> >::iterator p = permutedDiagCandidatesFiltered.begin();
          while(p != permutedDiagCandidatesFiltered.end() )
          {
            if((*p).second == globColId)
              p = permutedDiagCandidatesFiltered.erase(p);
            else
              p++;
          }
        }

      } // end if isNodeGlobalElement
    } // end loop over global_procOverlappingWeights and eliminate wrong entries...
  } // end if globalMultColRequests > 0

  // put together all pairs:
  //size_t sizeRowColPairs = keepDiagonalEntries.size() + permutedDiagCandidatesFiltered.size();
  std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> > RowColPairs;
  RowColPairs.insert( RowColPairs.end(), keepDiagonalEntries.begin(), keepDiagonalEntries.end());
  RowColPairs.insert( RowColPairs.end(), permutedDiagCandidatesFiltered.begin(), permutedDiagCandidatesFiltered.end());

#ifdef DEBUG_OUTPUT
  //&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
  // plausibility check
  gColVec->putScalar(0.0);
  gDomVec->putScalar(0.0);
  typename std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> >::iterator pl = RowColPairs.begin();
  while(pl != RowColPairs.end() )
  {
    //GlobalOrdinal ik = (*pl).first;
    GlobalOrdinal jk = (*pl).second;

    gColVec->sumIntoGlobalValue(jk,1.0);
    pl++;
  }
  gDomVec->doExport(*gColVec,*exporter,Xpetra::ADD);
  for(size_t sz = 0; sz<gDomVec->getLocalLength(); ++sz) {
    Teuchos::ArrayRCP< const Scalar > arrDomVec = gDomVec->getData(0);
    if(arrDomVec[sz] > 1.0) {
      GetOStream(Runtime0,0) << "RowColPairs has multiple column [" << sz << "]=" << arrDomVec[sz] << std::endl;
    } else if(arrDomVec[sz] == 0.0) {
      GetOStream(Runtime0,0) << "RowColPairs has empty column [" << sz << "]=" << arrDomVec[sz] << std::endl;
    }
  }
  //&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
#endif

  //////////////////////////////////////////////////
  // assumption: on each processor RowColPairs now contains
  // a valid set of (row,column) pairs, where the row entries
  // are a subset of the processor's rows and the column entries
  // are unique throughout all processors.
  // Note: the RowColPairs are only defined for a subset of all rows,
  // so there might be rows without an entry in RowColPairs.
  // It can be, that some rows seem to be missing in RowColPairs, since
  // the entry in that row with maximum absolute value has been reserved
  // by another row already (e.g. as already diagonal dominant row outside
  // of perRowMap).
  // In fact, the RowColPairs vector only defines the (row,column) pairs
  // that will be definitely moved to the diagonal after permutation.

#ifdef DEBUG_OUTPUT
  //  for (typename std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> >::const_iterator p = RowColPairs.begin(); p != RowColPairs.end(); ++p) {
  //    std::cout << "proc: " << myRank << " r/c: " << (*p).first << "/" << (*p).second << std::endl;
  //  }
  //    for (typename std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> >::const_iterator p = RowColPairs.begin(); p != RowColPairs.end(); ++p)
  //    {
  ////      if((*p).first != (*p).second) std::cout << "difference: " << (*p).first << " " << (*p).second << std::endl;
  //      std::cout << (*p).first +1 << " " << (*p).second+1 << std::endl;
  //    }
  //    std::cout << "\n";
#endif

  // vectors to store permutation information
  Teuchos::RCP<Vector> Pperm  = VectorFactory::Build(A->getRowMap());
  Teuchos::RCP<Vector> Qperm  = VectorFactory::Build(A->getDomainMap()); // global variant (based on domain map)
  Teuchos::RCP<Vector> lQperm = VectorFactory::Build(A->getColMap());  // local variant (based on column map)

  Teuchos::ArrayRCP< Scalar > PpermData = Pperm->getDataNonConst(0);
  Teuchos::ArrayRCP< Scalar > QpermData = Qperm->getDataNonConst(0);

  Pperm->putScalar(0.0);
  Qperm->putScalar(0.0);
  lQperm->putScalar(0.0);

  // setup exporter for Qperm
  Teuchos::RCP<Export> QpermExporter = ExportFactory::Build(lQperm->getMap(), Qperm->getMap());

  Teuchos::RCP<Vector> RowIdStatus  = VectorFactory::Build(A->getRowMap());
  Teuchos::RCP<Vector> ColIdStatus  = VectorFactory::Build(A->getDomainMap()); // global variant (based on domain map)
  Teuchos::RCP<Vector> lColIdStatus = VectorFactory::Build(A->getColMap()); // local variant (based on column map)
  Teuchos::RCP<Vector> ColIdUsed   = VectorFactory::Build(A->getDomainMap()); // mark column ids to be already in use
  Teuchos::ArrayRCP< Scalar > RowIdStatusArray = RowIdStatus->getDataNonConst(0);
  Teuchos::ArrayRCP< Scalar > ColIdStatusArray = ColIdStatus->getDataNonConst(0);
  Teuchos::ArrayRCP< Scalar > lColIdStatusArray = lColIdStatus->getDataNonConst(0);
  Teuchos::ArrayRCP< Scalar > ColIdUsedArray   = ColIdUsed->getDataNonConst(0); // not sure about this
  RowIdStatus->putScalar(0.0);
  ColIdStatus->putScalar(0.0);
  lColIdStatus->putScalar(0.0);
  ColIdUsed->putScalar(0.0);   // no column ids are used

  // count wide-range permutations
  // a wide-range permutation is defined as a permutation of rows/columns which do not
  // belong to the same node
  LocalOrdinal lWideRangeRowPermutations = 0;
  GlobalOrdinal gWideRangeRowPermutations = 0;
  LocalOrdinal lWideRangeColPermutations = 0;
  GlobalOrdinal gWideRangeColPermutations = 0;

  // run 1: mark all "identity" permutations
  typename std::vector<std::pair<GlobalOrdinal, GlobalOrdinal> >::iterator p = RowColPairs.begin();
  while(p != RowColPairs.end() )
  {
    GlobalOrdinal ik = (*p).first;
    GlobalOrdinal jk = (*p).second;

    LocalOrdinal lik = A->getRowMap()->getLocalElement(ik);
    LocalOrdinal ljk = A->getColMap()->getLocalElement(jk);

    if(RowIdStatusArray[lik] == 0.0) {
      RowIdStatusArray[lik] = 1.0; // use this row id
      lColIdStatusArray[ljk] = 1.0; // use this column id
      Pperm->replaceLocalValue(lik, ik);
      lQperm->replaceLocalValue(ljk, ik); // use column map
      ColIdUsed->replaceGlobalValue(ik,1.0); // ik is now used
      p = RowColPairs.erase(p);

      // detect wide range permutations
      if(floor(ik/nDofsPerNode) != floor(jk/nDofsPerNode)) {
        lWideRangeColPermutations++;
      }
    }
    else
      p++;
  }

  // communicate column map -> domain map
  Qperm->doExport(*lQperm,*QpermExporter,Xpetra::ABSMAX);
  ColIdStatus->doExport(*lColIdStatus,*QpermExporter,Xpetra::ABSMAX);

  // plausibility check
  if(RowColPairs.size()>0) GetOStream(Warnings0,0) << "MueLu::PermutationFactory: There are Row/Col pairs left!!!" << std::endl; // TODO fix me

  // close Pperm

  // count, how many row permutations are missing on current proc
  size_t cntFreeRowIdx = 0;
  std::queue<GlobalOrdinal> qFreeGRowIdx;  // store global row ids of "free" rows
  for (size_t lik = 0; lik < RowIdStatus->getLocalLength(); ++lik) {
    if(RowIdStatusArray[lik] == 0.0) {
      cntFreeRowIdx++;
      qFreeGRowIdx.push(RowIdStatus->getMap()->getGlobalElement(lik));
    }
  }

  // fix Pperm
  for (size_t lik = 0; lik < RowIdStatus->getLocalLength(); ++lik) {
    if(RowIdStatusArray[lik] == 0.0) {
      RowIdStatusArray[lik] = 1.0; // use this row id
      Pperm->replaceLocalValue(lik, qFreeGRowIdx.front());
      // detect wide range permutations
      if(floor(qFreeGRowIdx.front()/nDofsPerNode) != floor(RowIdStatus->getMap()->getGlobalElement(lik)/nDofsPerNode)) {
        lWideRangeRowPermutations++;
      }
      qFreeGRowIdx.pop();
    }
  }

  // close Qperm (free permutation entries in Qperm)
  size_t cntFreeColIdx = 0;
  std::queue<GlobalOrdinal> qFreeGColIdx;  // store global column ids of "free" available columns
  for (size_t ljk = 0; ljk < ColIdStatus->getLocalLength(); ++ljk) {
    if(ColIdStatusArray[ljk] == 0.0) {
      cntFreeColIdx++;
      qFreeGColIdx.push(ColIdStatus->getMap()->getGlobalElement(ljk));
    }
  }

  size_t cntUnusedColIdx = 0;
  std::queue<GlobalOrdinal> qUnusedGColIdx;  // store global column ids of "free" available columns
  for (size_t ljk = 0; ljk < ColIdUsed->getLocalLength(); ++ljk) {
    if(ColIdUsedArray[ljk] == 0.0) {
      cntUnusedColIdx++;
      qUnusedGColIdx.push(ColIdUsed->getMap()->getGlobalElement(ljk));
    }
  }

  // fix Qperm with local entries
  for (size_t ljk = 0; ljk < ColIdStatus->getLocalLength(); ++ljk) {
    // stop if no (local) unused column idx are left
    if(cntUnusedColIdx == 0) break;

    if(ColIdStatusArray[ljk] == 0.0) {
      ColIdStatusArray[ljk] = 1.0; // use this row id
      Qperm->replaceLocalValue(ljk, qUnusedGColIdx.front()); // loop over ColIdStatus (lives on domain map)
      ColIdUsed->replaceGlobalValue(qUnusedGColIdx.front(),1.0); // ljk is now used, too
      // detect wide range permutations
      if(floor(qUnusedGColIdx.front()/nDofsPerNode) != floor(ColIdStatus->getMap()->getGlobalElement(ljk)/nDofsPerNode)) {
        lWideRangeColPermutations++;
      }
      qUnusedGColIdx.pop();
      cntUnusedColIdx--;
      cntFreeColIdx--;
    }
  }

  //Qperm->doExport(*lQperm,*QpermExporter,Xpetra::ABSMAX); // no export necessary, since changes only locally
  //ColIdStatus->doExport(*lColIdStatus,*QpermExporter,Xpetra::ABSMAX);

  // count, how many unused column idx are needed on current processor
  // to complete Qperm
  cntFreeColIdx = 0;
  for (size_t ljk = 0; ljk < ColIdStatus->getLocalLength(); ++ljk) { // TODO avoid this loop
    if(ColIdStatusArray[ljk] == 0.0) {
      cntFreeColIdx++;
    }
  }

  GlobalOrdinal global_cntFreeColIdx = 0;
  LocalOrdinal  local_cntFreeColIdx = cntFreeColIdx;
  sumAll(comm, Teuchos::as<GlobalOrdinal>(local_cntFreeColIdx), global_cntFreeColIdx);
#ifdef DEBUG_OUTPUT
  std::cout << "global # of empty column idx entries in Qperm: " << global_cntFreeColIdx << std::endl;
#endif

  // avoid global communication if possible
  if(global_cntFreeColIdx > 0) {

    // 1) count how many unused column ids are left
    GlobalOrdinal global_cntUnusedColIdx = 0;
    LocalOrdinal  local_cntUnusedColIdx = cntUnusedColIdx;
    sumAll(comm, Teuchos::as<GlobalOrdinal>(local_cntUnusedColIdx), global_cntUnusedColIdx);
#ifdef DEBUG_OUTPUT
    std::cout << "global # of unused column idx: " << global_cntUnusedColIdx << std::endl;
#endif

    // 2) communicate how many unused column ids are available on procs
    std::vector<LocalOrdinal> local_UnusedColIdxOnProc (numProcs);
    std::vector<LocalOrdinal> global_UnusedColIdxOnProc(numProcs);
    local_UnusedColIdxOnProc[myRank] = local_cntUnusedColIdx;
    Teuchos::reduceAll(*comm, Teuchos::REDUCE_MAX, numProcs, &local_UnusedColIdxOnProc[0], &global_UnusedColIdxOnProc[0]);

#ifdef DEBUG_OUTPUT
    std::cout << "PROC " << myRank << " global num unused indices per proc: ";
    for (size_t ljk = 0; ljk < global_UnusedColIdxOnProc.size(); ++ljk) {
      std::cout << " " << global_UnusedColIdxOnProc[ljk];
    }
    std::cout << std::endl;
#endif

    // 3) build array of length global_cntUnusedColIdx to globally replicate unused column idx
    std::vector<GlobalOrdinal> local_UnusedColIdxVector(Teuchos::as<size_t>(global_cntUnusedColIdx));
    std::vector<GlobalOrdinal> global_UnusedColIdxVector(Teuchos::as<size_t>(global_cntUnusedColIdx));
    GlobalOrdinal global_cntUnusedColIdxStartIter = 0;
    for(int proc=0; proc<myRank; proc++) {
      global_cntUnusedColIdxStartIter += global_UnusedColIdxOnProc[proc];
    }
    for(GlobalOrdinal k = global_cntUnusedColIdxStartIter; k < global_cntUnusedColIdxStartIter+local_cntUnusedColIdx; k++) {
      local_UnusedColIdxVector[k] = qUnusedGColIdx.front();
      qUnusedGColIdx.pop();
    }
    Teuchos::reduceAll(*comm, Teuchos::REDUCE_MAX, Teuchos::as<int>(global_cntUnusedColIdx), &local_UnusedColIdxVector[0], &global_UnusedColIdxVector[0]);
#ifdef DEBUG_OUTPUT
    std::cout << "PROC " << myRank << " global UnusedGColIdx: ";
    for (size_t ljk = 0; ljk < global_UnusedColIdxVector.size(); ++ljk) {
      std::cout << " " << global_UnusedColIdxVector[ljk];
    }
    std::cout << std::endl;
#endif



    // 4) communicate, how many column idx are needed on each processor
    //    to complete Qperm
    std::vector<LocalOrdinal> local_EmptyColIdxOnProc (numProcs);
    std::vector<LocalOrdinal> global_EmptyColIdxOnProc(numProcs);
    local_EmptyColIdxOnProc[myRank] = local_cntFreeColIdx;
    Teuchos::reduceAll(*comm, Teuchos::REDUCE_MAX, numProcs, &local_EmptyColIdxOnProc[0], &global_EmptyColIdxOnProc[0]);

#ifdef DEBUG_OUTPUT
    std::cout << "PROC " << myRank << " global num of needed column indices: ";
    for (size_t ljk = 0; ljk < global_EmptyColIdxOnProc.size(); ++ljk) {
      std::cout << " " << global_EmptyColIdxOnProc[ljk];
    }
    std::cout << std::endl;
#endif

    // 5) determine first index in global_UnusedColIdxVector for unused column indices,
    //    that are marked to be used by this processor
    GlobalOrdinal global_UnusedColStartIdx = 0;
    for(int proc=0; proc<myRank; proc++) {
      global_UnusedColStartIdx += global_EmptyColIdxOnProc[proc];
    }

#ifdef DEBUG_OUTPUT
    GetOStream(Statistics0,0) << "PROC " << myRank << " is allowd to use the following column gids: ";
    for(GlobalOrdinal k = global_UnusedColStartIdx; k < global_UnusedColStartIdx + Teuchos::as<GlobalOrdinal>(cntFreeColIdx); k++) {
      GetOStream(Statistics0,0) << global_UnusedColIdxVector[k] << " ";
    }
    GetOStream(Statistics0,0) << std::endl;
#endif

    // 6.) fix Qperm with global entries
    GlobalOrdinal array_iter = 0;
    for (size_t ljk = 0; ljk < ColIdStatus->getLocalLength(); ++ljk) {

      if(ColIdStatusArray[ljk] == 0.0) {
        ColIdStatusArray[ljk] = 1.0; // use this row id
        Qperm->replaceLocalValue(ljk, global_UnusedColIdxVector[global_UnusedColStartIdx + array_iter]);
        ColIdUsed->replaceGlobalValue(global_UnusedColIdxVector[global_UnusedColStartIdx + array_iter],1.0);
        // detect wide range permutations
        if(floor(global_UnusedColIdxVector[global_UnusedColStartIdx + array_iter]/nDofsPerNode) != floor(ColIdStatus->getMap()->getGlobalElement(ljk)/nDofsPerNode)) {
          lWideRangeColPermutations++;
        }
        array_iter++;
        //cntUnusedColIdx--; // check me
      }
    }
  } // end if global_cntFreeColIdx > 0
  /////////////////// Qperm should be fine now...


  // create new empty Matrix
  Teuchos::RCP<CrsMatrixWrap> permPTmatrix = Teuchos::rcp(new CrsMatrixWrap(A->getRowMap(),1,Xpetra::StaticProfile));
  Teuchos::RCP<CrsMatrixWrap> permQTmatrix = Teuchos::rcp(new CrsMatrixWrap(A->getRowMap(),1,Xpetra::StaticProfile));

  for(size_t row=0; row<A->getNodeNumRows(); row++) {
    Teuchos::ArrayRCP<GlobalOrdinal> indoutP(1,Teuchos::as<GO>(PpermData[row])); // column idx for Perm^T
    Teuchos::ArrayRCP<GlobalOrdinal> indoutQ(1,Teuchos::as<GO>(QpermData[row])); // column idx for Qperm
    Teuchos::ArrayRCP<Scalar> valout(1,1.0);
    permPTmatrix->insertGlobalValues(A->getRowMap()->getGlobalElement(row), indoutP.view(0,indoutP.size()), valout.view(0,valout.size()));
    permQTmatrix->insertGlobalValues (A->getRowMap()->getGlobalElement(row), indoutQ.view(0,indoutQ.size()), valout.view(0,valout.size()));
  }

  permPTmatrix->fillComplete();
  permQTmatrix->fillComplete();

  Teuchos::RCP<Matrix> permPmatrix = Utils2::Transpose(permPTmatrix,true);

  for(size_t row=0; row<permPTmatrix->getNodeNumRows(); row++) {
    if(permPTmatrix->getNumEntriesInLocalRow(row) != 1)
      GetOStream(Warnings0,0) <<"#entries in row " << row << " of permPTmatrix is " << permPTmatrix->getNumEntriesInLocalRow(row) << std::endl;
    if(permPmatrix->getNumEntriesInLocalRow(row) != 1)
      GetOStream(Warnings0,0) <<"#entries in row " << row << " of permPmatrix is " << permPmatrix->getNumEntriesInLocalRow(row) << std::endl;
    if(permQTmatrix->getNumEntriesInLocalRow(row) != 1)
      GetOStream(Warnings0,0) <<"#entries in row " << row << " of permQmatrix is " << permQTmatrix->getNumEntriesInLocalRow(row) << std::endl;
  }

  // build permP * A * permQT
  Teuchos::RCP<Matrix> ApermQt = Utils::Multiply(*A, false, *permQTmatrix, false);
  Teuchos::RCP<Matrix> permPApermQt = Utils::Multiply(*permPmatrix, false, *ApermQt, false);

  /*
  MueLu::Utils<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps>::Write("A.mat", *A);
  MueLu::Utils<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps>::Write("permP.mat", *permPmatrix);
  MueLu::Utils<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps>::Write("permQt.mat", *permQTmatrix);
  MueLu::Utils<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps>::Write("permPApermQt.mat", *permPApermQt);
  */
  // build scaling matrix
  Teuchos::RCP<Vector> diagVec = VectorFactory::Build(permPApermQt->getRowMap(),true);
  Teuchos::RCP<Vector> invDiagVec = VectorFactory::Build(permPApermQt->getRowMap(),true);
  Teuchos::ArrayRCP< const Scalar > diagVecData = diagVec->getData(0);
  Teuchos::ArrayRCP< Scalar > invDiagVecData = invDiagVec->getDataNonConst(0);

  permPApermQt->getLocalDiagCopy(*diagVec);
  for(size_t i = 0; i<diagVec->getMap()->getNodeNumElements(); ++i) {
    if(diagVecData[i] != 0.0)
      invDiagVecData[i] = 1/diagVecData[i];
    else {
      invDiagVecData[i] = 1.0;
      GetOStream(Statistics0,0) << "MueLu::PermutationFactory: found zero on diagonal in row " << i << std::endl;
    }
  }

  Teuchos::RCP<CrsMatrixWrap> diagScalingOp = Teuchos::rcp(new CrsMatrixWrap(permPApermQt->getRowMap(),1,Xpetra::StaticProfile));

  for(size_t row=0; row<A->getNodeNumRows(); row++) {
    Teuchos::ArrayRCP<GlobalOrdinal> indout(1,permPApermQt->getRowMap()->getGlobalElement(row)); // column idx for Perm^T
    Teuchos::ArrayRCP<Scalar> valout(1,invDiagVecData[row]);
    diagScalingOp->insertGlobalValues(A->getRowMap()->getGlobalElement(row), indout.view(0,indout.size()), valout.view(0,valout.size()));
  }
  diagScalingOp->fillComplete();

  Teuchos::RCP<Matrix> scaledA = Utils::Multiply(*diagScalingOp, false, *permPApermQt, false);
  currentLevel.Set("A", Teuchos::rcp_dynamic_cast<Matrix>(scaledA), genFactory/*this*/);

  currentLevel.Set("permA", Teuchos::rcp_dynamic_cast<Matrix>(permPApermQt), genFactory/*this*/);  // TODO careful with this!!!
  currentLevel.Set("permP", Teuchos::rcp_dynamic_cast<Matrix>(permPmatrix), genFactory/*this*/);
  currentLevel.Set("permQT", Teuchos::rcp_dynamic_cast<Matrix>(permQTmatrix), genFactory/*this*/);
  currentLevel.Set("permScaling", Teuchos::rcp_dynamic_cast<Matrix>(diagScalingOp), genFactory/*this*/);

  //// count row permutations
  // count zeros on diagonal in P -> number of row permutations
  Teuchos::RCP<Vector> diagPVec = VectorFactory::Build(permPmatrix->getRowMap(),true);
  permPmatrix->getLocalDiagCopy(*diagPVec);
  Teuchos::ArrayRCP< const Scalar > diagPVecData = diagPVec->getData(0);
  LocalOrdinal lNumRowPermutations = 0;
  GlobalOrdinal gNumRowPermutations = 0;
  for(size_t i = 0; i<diagPVec->getMap()->getNodeNumElements(); ++i) {
    if(diagPVecData[i] == 0.0) {
      lNumRowPermutations++;
    }
  }

  // sum up all entries in multipleColRequests over all processors
  sumAll(diagPVec->getMap()->getComm(), Teuchos::as<GlobalOrdinal>(lNumRowPermutations), gNumRowPermutations);

  //// count column permutations
  // count zeros on diagonal in Q^T -> number of column permutations
  Teuchos::RCP<Vector> diagQTVec = VectorFactory::Build(permQTmatrix->getRowMap(),true);
  permQTmatrix->getLocalDiagCopy(*diagQTVec);
  Teuchos::ArrayRCP< const Scalar > diagQTVecData = diagQTVec->getData(0);
  LocalOrdinal lNumColPermutations = 0;
  GlobalOrdinal gNumColPermutations = 0;
  for(size_t i = 0; i<diagQTVec->getMap()->getNodeNumElements(); ++i) {
    if(diagQTVecData[i] == 0.0) {
      lNumColPermutations++;
    }
  }

  // sum up all entries in multipleColRequests over all processors
  sumAll(diagQTVec->getMap()->getComm(), Teuchos::as<GlobalOrdinal>(lNumColPermutations), gNumColPermutations);

  currentLevel.Set("#RowPermutations", gNumRowPermutations, genFactory/*this*/);
  currentLevel.Set("#ColPermutations", gNumColPermutations, genFactory/*this*/);
  currentLevel.Set("#WideRangeRowPermutations", gWideRangeRowPermutations, genFactory/*this*/);
  currentLevel.Set("#WideRangeColPermutations", gWideRangeColPermutations, genFactory/*this*/);

  GetOStream(Statistics0, 0) << "#Row    permutations/max possible permutations: " << gNumRowPermutations << "/" << diagPVec->getMap()->getGlobalNumElements() << std::endl;
  GetOStream(Statistics0, 0) << "#Column permutations/max possible permutations: " << gNumColPermutations << "/" << diagQTVec->getMap()->getGlobalNumElements() << std::endl;
  GetOStream(Runtime1, 0) << "#wide range row permutations: " << gWideRangeRowPermutations << " #wide range column permutations: " << gWideRangeColPermutations << std::endl;

#else
#warning PermutationFactory not compiling/working for Scalar==complex.
#endif // #ifndef HAVE_MUELU_INST_COMPLEX_INT_INT


  }
  void SubBlockAFactory<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps>::Build(Level & currentLevel) const {
    typedef Xpetra::Matrix<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps> OMatrix; //TODO
    typedef Xpetra::CrsMatrix<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps> CrsMatrixClass; //TODO
    typedef Xpetra::CrsMatrixWrap<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps> CrsMatrixWrapClass; //TODO
    typedef Xpetra::BlockedCrsMatrix<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps> BlockedCrsOMatrix; //TODO
    typedef Xpetra::MapExtractor<Scalar, LocalOrdinal, GlobalOrdinal, Node> MapExtractorClass;

    const ParameterList & pL = GetParameterList();
    size_t row = Teuchos::as<size_t>(pL.get<int>("block row"));
    size_t col = Teuchos::as<size_t>(pL.get<int>("block col"));

    RCP<OMatrix> Ain = Teuchos::null;
    Ain = Get< RCP<OMatrix> >(currentLevel, "A");

    RCP<BlockedCrsOMatrix> bA = Teuchos::rcp_dynamic_cast<BlockedCrsOMatrix>(Ain);

    TEUCHOS_TEST_FOR_EXCEPTION(bA==Teuchos::null, Exceptions::BadCast, "MueLu::SubBlockAFactory::Build: input matrix A is not of type BlockedCrsMatrix! error.");
    TEUCHOS_TEST_FOR_EXCEPTION(row > bA->Rows(), Exceptions::RuntimeError, "MueLu::SubBlockAFactory::Build: A.Rows() > rows_! error.");
    TEUCHOS_TEST_FOR_EXCEPTION(col > bA->Cols(), Exceptions::RuntimeError, "MueLu::SubBlockAFactory::Build: A.Cols() > cols_! error.");

    Teuchos::RCP<CrsMatrixClass> A = bA->getMatrix(row, col);

    Teuchos::RCP<CrsMatrixWrapClass> Op = Teuchos::rcp(new CrsMatrixWrapClass(A));

    //////////////// EXPERIMENTAL
    // extract striding information from RangeMapExtractor

    Teuchos::RCP<const MapExtractorClass> rgMapExtractor = bA->getRangeMapExtractor();
    Teuchos::RCP<const MapExtractorClass> doMapExtractor = bA->getDomainMapExtractor();

    Teuchos::RCP<const Map> rgMap = rgMapExtractor->getMap(row);
    Teuchos::RCP<const Map> doMap = doMapExtractor->getMap(col);

    Teuchos::RCP<const StridedMap> srgMap = Teuchos::rcp_dynamic_cast<const StridedMap>(rgMap);
    Teuchos::RCP<const StridedMap> sdoMap = Teuchos::rcp_dynamic_cast<const StridedMap>(doMap);

    if(srgMap == Teuchos::null) {
      Teuchos::RCP<const Map> fullRgMap = rgMapExtractor->getFullMap();
      Teuchos::RCP<const StridedMap> sFullRgMap = Teuchos::rcp_dynamic_cast<const StridedMap>(fullRgMap);
      TEUCHOS_TEST_FOR_EXCEPTION(sFullRgMap==Teuchos::null, Exceptions::BadCast, "MueLu::SubBlockAFactory::Build: full rangeMap is not a strided map");
      std::vector<size_t> stridedData = sFullRgMap->getStridingData();
      if(stridedData.size() == 1 && row > 0) // we have block matrices. use striding block information 0
        srgMap = StridedMapFactory::Build(rgMap, stridedData, 0, sFullRgMap->getOffset());
      else // we have strided matrices. use striding information of the corresponding block
        srgMap = StridedMapFactory::Build(rgMap, stridedData, row, sFullRgMap->getOffset());
    }

    if(sdoMap == Teuchos::null) {
      Teuchos::RCP<const Map> fullDoMap = doMapExtractor->getFullMap();
      Teuchos::RCP<const StridedMap> sFullDoMap = Teuchos::rcp_dynamic_cast<const StridedMap>(fullDoMap);
      TEUCHOS_TEST_FOR_EXCEPTION(sFullDoMap==Teuchos::null, Exceptions::BadCast, "MueLu::SubBlockAFactory::Build: full domainMap is not a strided map");
      std::vector<size_t> stridedData2 = sFullDoMap->getStridingData();
      if(stridedData2.size() == 1 && col > 0) // we have block matrices. use striding block information 0
        sdoMap = StridedMapFactory::Build(doMap, stridedData2, 0, sFullDoMap->getOffset());
      else // we have strided matrices. use striding information of the corresponding block
        sdoMap = StridedMapFactory::Build(doMap, stridedData2, col, sFullDoMap->getOffset());
    }

    TEUCHOS_TEST_FOR_EXCEPTION(srgMap==Teuchos::null, Exceptions::BadCast, "MueLu::SubBlockAFactory::Build: rangeMap " << row << " is not a strided map");
    TEUCHOS_TEST_FOR_EXCEPTION(sdoMap==Teuchos::null, Exceptions::BadCast, "MueLu::SubBlockAFactory::Build: domainMap " << col << " is not a strided map");

    GetOStream(Statistics1) << "A(" << row << "," << col << ") has strided maps: range map fixed block size=" << srgMap->getFixedBlockSize() << " strided block id = " << srgMap->getStridedBlockId() << ", domain map fixed block size=" << sdoMap->getFixedBlockSize() << ", strided block id=" << sdoMap->getStridedBlockId() << std::endl;

    if(Op->IsView("stridedMaps") == true) Op->RemoveView("stridedMaps");
    Op->CreateView("stridedMaps", srgMap, sdoMap);
    TEUCHOS_TEST_FOR_EXCEPTION(Op->IsView("stridedMaps")==false, Exceptions::RuntimeError, "MueLu::SubBlockAFactory::Build: failed to set stridedMaps");

    //////////////// EXPERIMENTAL

    currentLevel.Set("A", Teuchos::rcp_dynamic_cast<OMatrix>(Op), this);
  }
  void CloneRepartitionInterface<Scalar, LocalOrdinal, GlobalOrdinal, Node>::Build(Level &currentLevel) const {
    FactoryMonitor m(*this, "Build", currentLevel);
    currentLevel.print(GetOStream(Statistics0,0));
    // extract blocked operator A from current level
    Teuchos::RCP<Matrix> A = Get< Teuchos::RCP<Matrix> >     (currentLevel, "A");
    Teuchos::RCP<const Teuchos::Comm< int > > comm = A->getRowMap()->getComm();

    // number of Partitions only used for a shortcut.
    GO numPartitions = 0;
    if (currentLevel.IsAvailable("number of partitions")) {
      numPartitions = currentLevel.Get<GO>("number of partitions");
      GetOStream(Warnings0) << "Using user-provided \"number of partitions\", the performance is unknown" << std::endl;

    }

    // ======================================================================================================
    // Construct decomposition vector
    // ======================================================================================================
    RCP<GOVector> decomposition = Teuchos::null;

    // extract decomposition vector
    decomposition = Get<RCP<GOVector> >(currentLevel, "Partition");
    ArrayRCP<const GO> decompEntries = decomposition->getData(0);

    if (decomposition.is_null()) {
      GetOStream(Warnings0) << "No repartitioning necessary: partitions were left unchanged by the repartitioner" << std::endl;
      Set<RCP<const Import> >(currentLevel, "Importer", Teuchos::null);
      return;
    }

    // create new decomposition vector
    Teuchos::RCP<GOVector> ret = Xpetra::VectorFactory<GO, LO, GO, NO>::Build(A->getRowMap(), false);
    ArrayRCP<GO> retDecompEntries = ret->getDataNonConst(0);

    // block size of output vector
    LocalOrdinal blkSize = 1;

    // check for blocking/striding information
    if(A->IsView("stridedMaps") &&
       Teuchos::rcp_dynamic_cast<const StridedMap>(A->getRowMap("stridedMaps")) != Teuchos::null) {
      Xpetra::viewLabel_t oldView = A->SwitchToView("stridedMaps"); // note: "stridedMaps are always non-overlapping (correspond to range and domain maps!)
      RCP<const StridedMap> strMap = Teuchos::rcp_dynamic_cast<const StridedMap>(A->getRowMap());
      TEUCHOS_TEST_FOR_EXCEPTION(strMap == Teuchos::null,Exceptions::BadCast,"MueLu::CloneRepartitionInterface::Build: cast to strided row map failed.");
      LocalOrdinal stridedBlock = strMap->getStridedBlockId();
      if (stridedBlock == -1)
        blkSize = strMap->getFixedBlockSize();
      else {
        std::vector<size_t> strInfo = strMap->getStridingData();
        blkSize = strInfo[stridedBlock];
      }
      oldView = A->SwitchToView(oldView);
      GetOStream(Statistics1) << "CloneRepartitionInterface::Build():" << " found blockdim=" << blkSize << " from strided maps."<< std::endl;
    } else {
      GetOStream(Statistics1) << "CloneRepartitionInterface::Build(): no striding information available. Use blockdim=" << blkSize << " (DofsPerNode)." << std::endl;
      blkSize = A->GetFixedBlockSize();
    }

    // plausibility check!
    size_t inLocalLength  = decomposition->getLocalLength();
    size_t outLocalLength = A->getRowMap()->getNodeNumElements();

    // only for non-strided maps
    size_t numLocalNodes = outLocalLength / blkSize;
    TEUCHOS_TEST_FOR_EXCEPTION(Teuchos::as<size_t>(outLocalLength  % blkSize) != 0, MueLu::Exceptions::RuntimeError,"CloneRepartitionInterface: inconsistent number of local DOFs (" << outLocalLength << ") and degrees of freedoms (" << blkSize <<")");

    if (numLocalNodes > 0) {
      TEUCHOS_TEST_FOR_EXCEPTION(Teuchos::as<size_t>(inLocalLength  % numLocalNodes) != 0, MueLu::Exceptions::RuntimeError,"CloneRepartitionInterface: inconsistent number of local DOFs (" << inLocalLength << ") and number of local nodes (" << numLocalNodes << ")");
      LocalOrdinal inBlkSize = Teuchos::as<LocalOrdinal>(inLocalLength / numLocalNodes);
      //TEUCHOS_TEST_FOR_EXCEPTION(blkSize != inBlkSize, MueLu::Exceptions::RuntimeError,"CloneRepartitionInterface: input block size = " << inBlkSize << " outpub block size = " << blkSize << ". They should be the same.");

      for(LO i = 0; i<Teuchos::as<LO>(numLocalNodes); i++) {
        for(LO j = 0; j < blkSize; j++) {
          retDecompEntries[i*blkSize + j] = Teuchos::as<GO>(decompEntries[i*inBlkSize]);
        }
      }
    } // end if numLocalNodes > 0
    Set(currentLevel, "Partition", ret);
  } //Build()
  TEUCHOS_UNIT_TEST(CoalesceDropFactory, AmalgamationStridedOffsetDropping2LW)
  {
    // unit test for block size 9 = (2,3,4). wrap block 1.
    // drop small entries
    // lightweight wrap = true
    out << "version: " << MueLu::Version() << std::endl;

    RCP<const Teuchos::Comm<int> > comm = Parameters::getDefaultComm();
    Xpetra::UnderlyingLib lib = TestHelpers::Parameters::getLib();

    // create strided map information
    std::vector<size_t> stridingInfo;
    stridingInfo.push_back(as<size_t>(2));
    stridingInfo.push_back(as<size_t>(3));
    stridingInfo.push_back(as<size_t>(4));
    LocalOrdinal stridedBlockId = 1;
    GlobalOrdinal offset = 19;

    RCP<const StridedMap> dofMap = Xpetra::StridedMapFactory<LocalOrdinal, GlobalOrdinal, Node>::Build(lib, 9*comm->getSize(), 0,
                                  stridingInfo, comm,
                                  stridedBlockId, offset);

    /////////////////////////////////////////////////////

    Teuchos::RCP<Matrix> mtx = TestHelpers::TestFactory<SC,LO,GO,NO>::BuildTridiag(dofMap, 2.0, 1.0, 0.0001);

    Level fineLevel;
    TestHelpers::TestFactory<SC,LO,GO,NO>::createSingleLevelHierarchy(fineLevel);

    RCP<const Map> stridedRangeMap = Xpetra::StridedMapFactory<LocalOrdinal, GlobalOrdinal, Node>::Build(
                                                  mtx->getRangeMap(),
                                                  stridingInfo,
                                                  stridedBlockId,
                                                  offset
                                                  );
    RCP<const Map> stridedDomainMap = Xpetra::StridedMapFactory<LocalOrdinal, GlobalOrdinal, Node>::Build(
                                            mtx->getDomainMap(),
                                            stridingInfo,
                                            stridedBlockId,
                                            offset
                                            );

    if(mtx->IsView("stridedMaps") == true) mtx->RemoveView("stridedMaps");
    mtx->CreateView("stridedMaps", stridedRangeMap, stridedDomainMap);

    fineLevel.Set("A", mtx);
    CoalesceDropFactory dropFact = CoalesceDropFactory();
    dropFact.SetParameter("lightweight wrap",Teuchos::ParameterEntry(true));
    dropFact.SetParameter("aggregation: drop tol",Teuchos::ParameterEntry(0.3));

    fineLevel.Request("Graph", &dropFact);
    fineLevel.Request("DofsPerNode", &dropFact);

    dropFact.Build(fineLevel);

    fineLevel.print(out);
    RCP<GraphBase> graph = fineLevel.Get<RCP<GraphBase> >("Graph", &dropFact);

    LO myDofsPerNode = fineLevel.Get<LO>("DofsPerNode", &dropFact);
    TEST_EQUALITY(as<int>(graph->GetDomainMap()->getGlobalNumElements()) == comm->getSize(), true);
    TEST_EQUALITY(as<int>(myDofsPerNode) == 9, true);
    bool bCorrectGraph = false;
    if (comm->getSize() == 1 && graph->getNeighborVertices(0).size() == 1) {
      bCorrectGraph = true;
    } else {
      if (comm->getRank() == 0) {
        if (graph->getNeighborVertices(0).size() == 1) bCorrectGraph = true;
      }
      else {
        if (graph->getNeighborVertices(0).size() == 2) bCorrectGraph = true;
      }
    }
    TEST_EQUALITY(bCorrectGraph, true);

    const RCP<const Map> myImportMap = graph->GetImportMap(); // < note that the ImportMap is built from the column map of the matrix A WITHOUT dropping!
    const RCP<const Map> myDomainMap = graph->GetDomainMap();

    TEST_EQUALITY(myImportMap->getMaxAllGlobalIndex(), comm->getSize()-1);
    TEST_EQUALITY(myImportMap->getMinAllGlobalIndex(), 0);
    TEST_EQUALITY(myImportMap->getMinLocalIndex(),0);
    TEST_EQUALITY(myImportMap->getGlobalNumElements(),as<size_t>(comm->getSize()+2*(comm->getSize()-1)));
    if (comm->getSize()>1) {
      size_t numLocalRowMapElts = graph->GetNodeNumVertices();
      size_t numLocalImportElts = myImportMap->getNodeNumElements();
      if (comm->getRank() == 0 || comm->getRank() == comm->getSize()-1) {
        TEST_EQUALITY(as<bool>(numLocalImportElts==numLocalRowMapElts+1), true);
      } else {
        TEST_EQUALITY(as<bool>(numLocalImportElts==numLocalRowMapElts+2), true);
      }
    }
    TEST_EQUALITY(myDomainMap->getMaxAllGlobalIndex(), comm->getSize()-1);
    TEST_EQUALITY(myDomainMap->getMinAllGlobalIndex(), 0);
    TEST_EQUALITY(myDomainMap->getMinLocalIndex(),0);
    TEST_EQUALITY(myDomainMap->getGlobalNumElements(),as<size_t>(comm->getSize()));
    TEST_EQUALITY(as<bool>(myDomainMap->getNodeNumElements()==1), true);
  } // AmalgamationStridedOffsetDropping2LW
  TEUCHOS_UNIT_TEST(CoalesceDropFactory, AmalgamationStrided2LW)
  {
#   include "MueLu_UseShortNames.hpp"
    MUELU_TESTING_SET_OSTREAM;
    MUELU_TESTING_LIMIT_SCOPE(Scalar,GlobalOrdinal,NO);
    out << "version: " << MueLu::Version() << std::endl;

    // unit test for block size 3 = (2,1). wrap block 0
    // lightweight wrap = true

    RCP<const Teuchos::Comm<int> > comm = Parameters::getDefaultComm();
    Xpetra::UnderlyingLib lib = TestHelpers::Parameters::getLib();

    // create strided map information
    std::vector<size_t> stridingInfo;
    stridingInfo.push_back(as<size_t>(2));
    stridingInfo.push_back(as<size_t>(1));
    LocalOrdinal stridedBlockId = 0;

    int blockSize=3;

    RCP<const StridedMap> dofMap = Xpetra::StridedMapFactory<LocalOrdinal, GlobalOrdinal, Node>::Build(lib, blockSize*comm->getSize(), 0,
                                  stridingInfo, comm,
                                  stridedBlockId /*blockId*/, 0 /*offset*/);

    /////////////////////////////////////////////////////

    Teuchos::RCP<Matrix> mtx = TestHelpers::TestFactory<SC,LO,GO,NO>::BuildTridiag(dofMap, 2.0, -1.0, -1.0);

    Level fineLevel;
    TestHelpers::TestFactory<SC,LO,GO,NO>::createSingleLevelHierarchy(fineLevel);

    RCP<const Xpetra::StridedMap<LocalOrdinal, GlobalOrdinal, Node> > stridedRangeMap = Xpetra::StridedMapFactory<LocalOrdinal, GlobalOrdinal, Node>::Build(
                                                  mtx->getRangeMap(),
                                                  stridingInfo,
                                                  stridedBlockId,
                                                  0 /*offset*/
                                                  );
    RCP<const Map> stridedDomainMap = Xpetra::StridedMapFactory<LocalOrdinal, GlobalOrdinal, Node>::Build(
                                            mtx->getDomainMap(),
                                            stridingInfo,
                                            stridedBlockId,
                                            0 /*offset*/
                                            );
    if(mtx->IsView("stridedMaps") == true) mtx->RemoveView("stridedMaps");
    mtx->CreateView("stridedMaps", stridedRangeMap, stridedDomainMap);

    fineLevel.Set("A", mtx);
    CoalesceDropFactory dropFact = CoalesceDropFactory();
    dropFact.SetParameter("lightweight wrap",Teuchos::ParameterEntry(true));
    fineLevel.Request("Graph", &dropFact);
    fineLevel.Request("DofsPerNode", &dropFact);

    dropFact.Build(fineLevel);

    fineLevel.print(out);
    RCP<GraphBase> graph = fineLevel.Get<RCP<GraphBase> >("Graph", &dropFact);

    LO myDofsPerNode = fineLevel.Get<LO>("DofsPerNode", &dropFact);
    TEST_EQUALITY(as<int>(graph->GetDomainMap()->getGlobalNumElements()) == comm->getSize(), true);
    TEST_EQUALITY(as<int>(myDofsPerNode) == blockSize, true);
    bool bCorrectGraph = false;
    if (comm->getSize() == 1 && graph->getNeighborVertices(0).size() == 1) {
      bCorrectGraph = true;
    } else {
      if (comm->getRank() == 0 || comm->getRank() == comm->getSize()-1) {
        if (graph->getNeighborVertices(0).size() == 2) bCorrectGraph = true;
      }
      else {
        if (graph->getNeighborVertices(0).size() == blockSize) bCorrectGraph = true;
      }
    }
    TEST_EQUALITY(bCorrectGraph, true);

    const RCP<const Map> myImportMap = graph->GetImportMap(); // < note that the ImportMap is built from the column map of the matrix A WITHOUT dropping!
    const RCP<const Map> myDomainMap = graph->GetDomainMap();

    TEST_EQUALITY(myImportMap->getMaxAllGlobalIndex(), comm->getSize()-1);
    TEST_EQUALITY(myImportMap->getMinAllGlobalIndex(), 0);
    TEST_EQUALITY(myImportMap->getMinLocalIndex(),0);
    TEST_EQUALITY(myImportMap->getGlobalNumElements(),as<size_t>(comm->getSize()+2*(comm->getSize()-1)));
    if (comm->getSize()>1) {
      size_t numLocalRowMapElts = graph->GetNodeNumVertices();
      size_t numLocalImportElts = myImportMap->getNodeNumElements();
      if (comm->getRank() == 0 || comm->getRank() == comm->getSize()-1) {
        TEST_EQUALITY(as<bool>(numLocalImportElts==numLocalRowMapElts+1), true);
      } else {
        TEST_EQUALITY(as<bool>(numLocalImportElts==numLocalRowMapElts+2), true);
      }
    }
    if (comm->getSize()>1) {
      size_t numLocalRowMapElts = graph->GetNodeNumVertices();
      size_t maxLocalIndex = myImportMap->getMaxLocalIndex();
      if (comm->getRank() == 0 || comm->getRank() == comm->getSize()-1) {
        TEST_EQUALITY(as<bool>(maxLocalIndex==numLocalRowMapElts*blockSize-2), true);
      } else {
        TEST_EQUALITY(as<bool>(maxLocalIndex==numLocalRowMapElts*blockSize-1), true);
      }
    }

    TEST_EQUALITY(myDomainMap->getMaxAllGlobalIndex(), comm->getSize()-1);
    TEST_EQUALITY(myDomainMap->getMinAllGlobalIndex(), 0);
    TEST_EQUALITY(myDomainMap->getMinLocalIndex(),0);
    TEST_EQUALITY(myDomainMap->getMaxLocalIndex(),0);
    TEST_EQUALITY(myDomainMap->getGlobalNumElements(),as<size_t>(comm->getSize()));
    TEST_EQUALITY(as<bool>(myDomainMap->getNodeNumElements()==1), true);
  } // AmalgamationStrided2LW
void RebalanceBlockRestrictionFactory<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps>::Build(Level &fineLevel, Level &coarseLevel) const {
  FactoryMonitor m(*this, "Build", coarseLevel);
  //const Teuchos::ParameterList & pL = GetParameterList();

  RCP<Teuchos::FancyOStream> out = Teuchos::fancyOStream(Teuchos::rcpFromRef(std::cout));

  Teuchos::RCP<Matrix> originalTransferOp = Teuchos::null;
  originalTransferOp = Get< RCP<Matrix> >(coarseLevel, "R");

  RCP<Xpetra::BlockedCrsMatrix<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps> > bOriginalTransferOp = Teuchos::rcp_dynamic_cast<Xpetra::BlockedCrsMatrix<Scalar, LocalOrdinal, GlobalOrdinal, Node, LocalMatOps> >(originalTransferOp);
  TEUCHOS_TEST_FOR_EXCEPTION(bOriginalTransferOp==Teuchos::null, Exceptions::BadCast, "MueLu::RebalanceBlockTransferFactory::Build: input matrix P or R is not of type BlockedCrsMatrix! error.");

  // plausibility check
  TEUCHOS_TEST_FOR_EXCEPTION(bOriginalTransferOp->Rows() != 2,Exceptions::RuntimeError, "MueLu::RebalanceBlockTransferFactory::Build: number of block rows of transfer operator is not equal 2. error.");
  TEUCHOS_TEST_FOR_EXCEPTION(bOriginalTransferOp->Cols() != 2,Exceptions::RuntimeError, "MueLu::RebalanceBlockTransferFactory::Build: number of block columns of transfer operator is not equal 2. error.");

  // rebuild rebalanced blocked P operator
  std::vector<GO> fullRangeMapVector;
  std::vector<GO> fullDomainMapVector;
  std::vector<RCP<const Map> > subBlockRRangeMaps;
  std::vector<RCP<const Map> > subBlockRDomainMaps;
  subBlockRRangeMaps.reserve(bOriginalTransferOp->Rows());       // reserve size for block P operators
  subBlockRDomainMaps.reserve(bOriginalTransferOp->Cols());       // reserve size for block P operators

  std::vector<Teuchos::RCP<Matrix> > subBlockRebR;
  subBlockRebR.reserve(bOriginalTransferOp->Cols());

  int curBlockId = 0;
  Teuchos::RCP<const Import> rebalanceImporter = Teuchos::null;
  std::vector<Teuchos::RCP<const FactoryManagerBase> >::const_iterator it;
  for (it = FactManager_.begin(); it != FactManager_.end(); ++it) {
    // begin SubFactoryManager environment
    SetFactoryManager fineSFM  (rcpFromRef(fineLevel),   *it);
    SetFactoryManager coarseSFM(rcpFromRef(coarseLevel), *it);

    rebalanceImporter = coarseLevel.Get<Teuchos::RCP<const Import> >("Importer", (*it)->GetFactory("Importer").get());

    // extract matrix block
    Teuchos::RCP<CrsMatrix> Rmii = bOriginalTransferOp->getMatrix(curBlockId, curBlockId);
    Teuchos::RCP<CrsMatrixWrap> Rwii = Teuchos::rcp(new CrsMatrixWrap(Rmii));
    Teuchos::RCP<Matrix> Rii = Teuchos::rcp_dynamic_cast<Matrix>(Rwii);

    Teuchos::RCP<Matrix> rebRii;
    if(rebalanceImporter != Teuchos::null) {
      std::stringstream ss; ss << "Rebalancing restriction block R(" << curBlockId << "," << curBlockId << ")";
      SubFactoryMonitor m1(*this, ss.str(), coarseLevel);
      {
        SubFactoryMonitor subM(*this, "Rebalancing restriction -- fusedImport", coarseLevel);
        // Note: The 3rd argument says to use originalR's domain map.

        RCP<Map> dummy;
        rebRii = MatrixFactory::Build(Rii,*rebalanceImporter,dummy,rebalanceImporter->getTargetMap());
      }

      RCP<ParameterList> params = rcp(new ParameterList());
      params->set("printLoadBalancingInfo", true);
      std::stringstream ss2; ss2 << "R(" << curBlockId << "," << curBlockId << ") rebalanced:";
      GetOStream(Statistics0) << PerfUtils::PrintMatrixInfo(*rebRii, ss2.str(), params);
    } else {
      rebRii = Rii;
      RCP<ParameterList> params = rcp(new ParameterList());
      params->set("printLoadBalancingInfo", true);
      std::stringstream ss2; ss2 << "R(" << curBlockId << "," << curBlockId << ") not rebalanced:";
      GetOStream(Statistics0) << PerfUtils::PrintMatrixInfo(*rebRii, ss2.str(), params);
    }

    // fix striding information for rebalanced diagonal block rebRii
    RCP<const Xpetra::MapExtractor<Scalar, LocalOrdinal, GlobalOrdinal, Node> > rgRMapExtractor = bOriginalTransferOp->getRangeMapExtractor(); // original map extractor
    Teuchos::RCP<const StridedMap> orig_stridedRgMap = Teuchos::rcp_dynamic_cast<const StridedMap>(rgRMapExtractor->getMap(Teuchos::as<size_t>(curBlockId)));
    Teuchos::RCP<const Map> stridedRgMap = Teuchos::null;
    if(orig_stridedRgMap != Teuchos::null) {
      std::vector<size_t> stridingData = orig_stridedRgMap->getStridingData();
      Teuchos::ArrayView< const GlobalOrdinal > nodeRangeMapii = rebRii->getRangeMap()->getNodeElementList();
      stridedRgMap = StridedMapFactory::Build(
          originalTransferOp->getRangeMap()->lib(),
          Teuchos::OrdinalTraits<Xpetra::global_size_t>::invalid(),
          nodeRangeMapii,
          rebRii->getRangeMap()->getIndexBase(),
          stridingData,
          originalTransferOp->getRangeMap()->getComm(),
          orig_stridedRgMap->getStridedBlockId(),
          orig_stridedRgMap->getOffset());
    }
    RCP<const Xpetra::MapExtractor<Scalar, LocalOrdinal, GlobalOrdinal, Node> > doRMapExtractor = bOriginalTransferOp->getDomainMapExtractor(); // original map extractor
    Teuchos::RCP<const StridedMap> orig_stridedDoMap = Teuchos::rcp_dynamic_cast<const StridedMap>(doRMapExtractor->getMap(Teuchos::as<size_t>(curBlockId)));
    Teuchos::RCP<const Map> stridedDoMap = Teuchos::null;
    if(orig_stridedDoMap != Teuchos::null) {
      std::vector<size_t> stridingData = orig_stridedDoMap->getStridingData();
      Teuchos::ArrayView< const GlobalOrdinal > nodeDomainMapii = rebRii->getDomainMap()->getNodeElementList();
      stridedDoMap = StridedMapFactory::Build(
          originalTransferOp->getDomainMap()->lib(),
          Teuchos::OrdinalTraits<Xpetra::global_size_t>::invalid(),
          nodeDomainMapii,
          rebRii->getDomainMap()->getIndexBase(),
          stridingData,
          originalTransferOp->getDomainMap()->getComm(),
          orig_stridedDoMap->getStridedBlockId(),
          orig_stridedDoMap->getOffset());
    }

    TEUCHOS_TEST_FOR_EXCEPTION(stridedRgMap == Teuchos::null,Exceptions::RuntimeError, "MueLu::RebalanceBlockRestrictionFactory::Build: failed to generate striding information. error.");
    TEUCHOS_TEST_FOR_EXCEPTION(stridedDoMap == Teuchos::null,Exceptions::RuntimeError, "MueLu::RebalanceBlockRestrictionFactory::Build: failed to generate striding information. error.");

    // replace stridedMaps view in diagonal sub block
    if(rebRii->IsView("stridedMaps")) rebRii->RemoveView("stridedMaps");
    rebRii->CreateView("stridedMaps", stridedRgMap, stridedDoMap);

    // store rebalanced subblock
    subBlockRebR.push_back(rebRii);

    // append strided row map (= range map) to list of range maps.
    Teuchos::RCP<const Map> rangeMapii = rebRii->getRowMap("stridedMaps"); //rebRii->getRangeMap();
    subBlockRRangeMaps.push_back(rangeMapii);
    Teuchos::ArrayView< const GlobalOrdinal > nodeRangeMapii = rebRii->getRangeMap()->getNodeElementList();
    fullRangeMapVector.insert(fullRangeMapVector.end(), nodeRangeMapii.begin(), nodeRangeMapii.end());
    sort(fullRangeMapVector.begin(), fullRangeMapVector.end());

    // append strided col map (= domain map) to list of range maps.
    Teuchos::RCP<const Map> domainMapii = rebRii->getColMap("stridedMaps"); //rebRii->getDomainMap();
    subBlockRDomainMaps.push_back(domainMapii);
    Teuchos::ArrayView< const GlobalOrdinal > nodeDomainMapii = rebRii->getDomainMap()->getNodeElementList();
    fullDomainMapVector.insert(fullDomainMapVector.end(), nodeDomainMapii.begin(), nodeDomainMapii.end());
    sort(fullDomainMapVector.begin(), fullDomainMapVector.end());

    ////////////////////////////////////////////////////////////

    // rebalance null space
    if(rebalanceImporter != Teuchos::null)
    { // rebalance null space
      std::stringstream ss2; ss2 << "Rebalancing nullspace block(" << curBlockId << "," << curBlockId << ")";
      SubFactoryMonitor subM(*this, ss2.str(), coarseLevel);

      RCP<MultiVector> nullspace = coarseLevel.Get<RCP<MultiVector> >("Nullspace", (*it)->GetFactory("Nullspace").get());
      RCP<MultiVector> permutedNullspace = MultiVectorFactory::Build(rebalanceImporter->getTargetMap(), nullspace->getNumVectors());
      permutedNullspace->doImport(*nullspace, *rebalanceImporter, Xpetra::INSERT);

      // TODO think about this
      //if (pL.get<bool>("useSubcomm") == true) // TODO either useSubcomm is enabled everywhere or nowhere
      //permutedNullspace->replaceMap(permutedNullspace->getMap()->removeEmptyProcesses());

      coarseLevel.Set<RCP<MultiVector> >("Nullspace", permutedNullspace, (*it)->GetFactory("Nullspace").get());

    } // end rebalance null space
    else { // do nothing
      RCP<MultiVector> nullspace = coarseLevel.Get<RCP<MultiVector> >("Nullspace", (*it)->GetFactory("Nullspace").get());
      coarseLevel.Set<RCP<MultiVector> >("Nullspace", nullspace, (*it)->GetFactory("Nullspace").get());
    }

    ////////////////////////////////////////////////////////////

    curBlockId++;
  } // end for loop

  // extract map index base from maps of blocked P
  GO rangeIndexBase = originalTransferOp->getRangeMap()->getIndexBase();
  GO domainIndexBase= originalTransferOp->getDomainMap()->getIndexBase();

  // check this
  RCP<const Xpetra::MapExtractor<Scalar, LocalOrdinal, GlobalOrdinal, Node> > rangeRMapExtractor = bOriginalTransferOp->getRangeMapExtractor(); // original map extractor
  Teuchos::ArrayView<GO> fullRangeMapGIDs(&fullRangeMapVector[0],fullRangeMapVector.size());
  Teuchos::RCP<const StridedMap> stridedRgFullMap = Teuchos::rcp_dynamic_cast<const StridedMap>(rangeRMapExtractor->getFullMap());
  Teuchos::RCP<const Map > fullRangeMap = Teuchos::null;
  if(stridedRgFullMap != Teuchos::null) {
    std::vector<size_t> stridedData = stridedRgFullMap->getStridingData();
    fullRangeMap =
        StridedMapFactory::Build(
            originalTransferOp->getRangeMap()->lib(),
            Teuchos::OrdinalTraits<Xpetra::global_size_t>::invalid(),
            fullRangeMapGIDs,
            rangeIndexBase,
            stridedData,
            originalTransferOp->getRangeMap()->getComm(),
            stridedRgFullMap->getStridedBlockId(),
            stridedRgFullMap->getOffset());
  } else {
    fullRangeMap =
        MapFactory::Build(
            originalTransferOp->getRangeMap()->lib(),
            Teuchos::OrdinalTraits<Xpetra::global_size_t>::invalid(),
            fullRangeMapGIDs,
            rangeIndexBase,
            originalTransferOp->getRangeMap()->getComm());
  }

  RCP<const Xpetra::MapExtractor<Scalar, LocalOrdinal, GlobalOrdinal, Node> > domainAMapExtractor = bOriginalTransferOp->getDomainMapExtractor();
  Teuchos::ArrayView<GO> fullDomainMapGIDs(&fullDomainMapVector[0],fullDomainMapVector.size());
  Teuchos::RCP<const StridedMap> stridedDoFullMap = Teuchos::rcp_dynamic_cast<const StridedMap>(domainAMapExtractor->getFullMap());
  Teuchos::RCP<const Map > fullDomainMap = Teuchos::null;
  if(stridedDoFullMap != Teuchos::null) {
    TEUCHOS_TEST_FOR_EXCEPTION(stridedDoFullMap==Teuchos::null, Exceptions::BadCast, "MueLu::BlockedPFactory::Build: full map in domain map extractor has no striding information! error.");
    std::vector<size_t> stridedData2 = stridedDoFullMap->getStridingData();
    fullDomainMap =
        StridedMapFactory::Build(
            originalTransferOp->getDomainMap()->lib(),
            Teuchos::OrdinalTraits<Xpetra::global_size_t>::invalid(),
            fullDomainMapGIDs,
            domainIndexBase,
            stridedData2,
            originalTransferOp->getDomainMap()->getComm(),
            stridedDoFullMap->getStridedBlockId(),
            stridedDoFullMap->getOffset());
  } else {

    fullDomainMap =
        MapFactory::Build(
            originalTransferOp->getDomainMap()->lib(),
            Teuchos::OrdinalTraits<Xpetra::global_size_t>::invalid(),
            fullDomainMapGIDs,
            domainIndexBase,
            originalTransferOp->getDomainMap()->getComm());
  }

  // build map extractors
  Teuchos::RCP<const Xpetra::MapExtractor<Scalar, LocalOrdinal, GlobalOrdinal, Node> > rangeMapExtractor  =
      Xpetra::MapExtractorFactory<Scalar, LocalOrdinal, GlobalOrdinal, Node>::Build(fullRangeMap,  subBlockRRangeMaps);
  Teuchos::RCP<const Xpetra::MapExtractor<Scalar, LocalOrdinal, GlobalOrdinal, Node> > domainMapExtractor =
      Xpetra::MapExtractorFactory<Scalar, LocalOrdinal, GlobalOrdinal, Node>::Build(fullDomainMap, subBlockRDomainMaps);

  Teuchos::RCP<BlockedCrsMatrix> bRebR = Teuchos::rcp(new BlockedCrsMatrix(rangeMapExtractor,domainMapExtractor,10));
  for(size_t i = 0; i<subBlockRRangeMaps.size(); i++) {
    Teuchos::RCP<const CrsMatrixWrap> crsOpii = Teuchos::rcp_dynamic_cast<const CrsMatrixWrap>(subBlockRebR[i]);
    Teuchos::RCP<CrsMatrix> crsMatii = crsOpii->getCrsMatrix();
    bRebR->setMatrix(i,i,crsMatii);
  }

  bRebR->fillComplete();

  Set(coarseLevel, "R", Teuchos::rcp_dynamic_cast<Matrix>(bRebR)); // do nothing  // TODO remove this!

} // Build