Ifpack_SingletonFilter.cpp

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//       Ifpack: Object-Oriented Algebraic Preconditioner Package
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#include "Ifpack_ConfigDefs.h"
#include "Ifpack_SingletonFilter.h"
#include "Epetra_ConfigDefs.h"
#include "Epetra_RowMatrix.h"
#include "Epetra_Comm.h"
#include "Epetra_Map.h"
#include "Epetra_MultiVector.h"
#include "Epetra_Vector.h"
#include "Epetra_Import.h"

//==============================================================================
Ifpack_SingletonFilter::Ifpack_SingletonFilter(const Teuchos::RefCountPtr<Epetra_RowMatrix>& Matrix) :
  A_(Matrix),
  NumSingletons_(0),
  NumRows_(0),
  NumRowsA_(0),
  MaxNumEntries_(0),
  MaxNumEntriesA_(0),
  NumNonzeros_(0)
{
  using std::cerr;
  using std::endl;

  // use this filter only on serial matrices
  if (A_->Comm().NumProc() != 1) {
    cerr << "Ifpack_SingletonFilter can be used with Comm().NumProc() == 1" << endl;
    cerr << "only. This class is a tool for Ifpack_AdditiveSchwarz," << endl;
    cerr << "and it is not meant to be used otherwise." << endl;
    exit(EXIT_FAILURE);
  }

  if ((A_->NumMyRows() != A_->NumGlobalRows64()) ||
     (A_->NumMyRows() != A_->NumMyCols()))
    IFPACK_CHK_ERRV(-1);

  NumRowsA_ = (A_->NumMyRows());
  MaxNumEntriesA_ = A_->MaxNumEntries();

  Indices_.resize(MaxNumEntriesA_);
  Values_.resize(MaxNumEntriesA_);
  Reorder_.resize(A_->NumMyRows());

  for (int i = 0 ; i < NumRowsA_ ; ++i)
    Reorder_[i] = -1;

  // first check how may singletons I do have
  for (int i = 0 ; i < NumRowsA_ ; ++i) {
    int Nnz;
    IFPACK_CHK_ERRV(A_->ExtractMyRowCopy(i,MaxNumEntriesA_,Nnz,
                                        &Values_[0], &Indices_[0]));
    if (Nnz != 1) {
      Reorder_[i] = NumRows_++;
    }
    else {
      NumSingletons_++;
    }
  }

  InvReorder_.resize(NumRows_);
  for (int i = 0 ; i < NumRowsA_ ; ++i) {
    if (Reorder_[i] < 0)
      continue;
    InvReorder_[Reorder_[i]] = i;
  }

  NumEntries_.resize(NumRows_);
  SingletonIndex_.resize(NumSingletons_);

  // now compute the nonzeros per row
  int count = 0;
  for (int i = 0 ; i < A_->NumMyRows() ; ++i) {

    int Nnz;
    IFPACK_CHK_ERRV(A_->ExtractMyRowCopy(i,MaxNumEntriesA_,Nnz,
                                          &Values_[0], &Indices_[0]));
    int ii = Reorder_[i];
    if (ii >= 0) {
      assert (Nnz != 1);

      NumEntries_[ii] = Nnz;
      NumNonzeros_ += Nnz;
      if (Nnz > MaxNumEntries_)
        MaxNumEntries_ = Nnz;
    }
    else {
      SingletonIndex_[count] = i;
      count++;
    }
  }

#if !defined(EPETRA_NO_32BIT_GLOBAL_INDICES) || !defined(EPETRA_NO_64BIT_GLOBAL_INDICES)
  Map_ = Teuchos::rcp( new Epetra_Map(NumRows_,0,Comm()) );
#endif

  // and finish up with the diagonal entry
  Diagonal_ = Teuchos::rcp( new Epetra_Vector(*Map_) );

  Epetra_Vector Diagonal(A_->Map());
  A_->ExtractDiagonalCopy(Diagonal);
  for (int i = 0 ; i < NumRows_ ; ++i) {
    int ii = InvReorder_[i];
    (*Diagonal_)[i] = Diagonal[ii];
  }

}

//==============================================================================
int Ifpack_SingletonFilter::
ExtractMyRowCopy(int MyRow, int Length, int & NumEntries,
                 double *Values, int * Indices) const
{
  int Nnz;

  if (Length < NumEntries_[MyRow])
    IFPACK_CHK_ERR(-1);

  int Row = InvReorder_[MyRow];
  IFPACK_CHK_ERR(A_->ExtractMyRowCopy(Row,MaxNumEntriesA_,Nnz,
                                     &Values_[0],&Indices_[0]));
  NumEntries = 0;
  for (int i = 0 ; i < Nnz ; ++i) {
    int ii = Reorder_[Indices_[i]];
    if ( ii >= 0) {
      Indices[NumEntries] = ii;
      Values[NumEntries] = Values_[i];
      NumEntries++;
    }
  }
  return(0);
}

//==============================================================================
int Ifpack_SingletonFilter::
ExtractDiagonalCopy(Epetra_Vector & Diagonal) const
{
  Diagonal = *Diagonal_;
  return(0);
}

//==============================================================================
int Ifpack_SingletonFilter::
Multiply(bool TransA, const Epetra_MultiVector& X,
         Epetra_MultiVector& Y) const
{

  int NumVectors = X.NumVectors();
  if (NumVectors != Y.NumVectors())
    IFPACK_CHK_ERR(-1);

  Y.PutScalar(0.0);

  std::vector<int> Indices(MaxNumEntries_);
  std::vector<double> Values(MaxNumEntries_);

  // cycle over all rows of the original matrix
  for (int i = 0 ; i < A_->NumMyRows() ; ++i) {

    if (Reorder_[i] < 0)
      continue; // skip singleton rows

    int Nnz;
    A_->ExtractMyRowCopy(i,MaxNumEntriesA_,Nnz,
                     &Values[0], &Indices[0]);
    if (!TransA) {
      // no transpose first
      for (int j = 0 ; j < NumVectors ; ++j) {
        for (int k = 0 ; k < Nnz ; ++k) {
          if (Reorder_[i] >= 0)
            Y[j][i] += Values[k] * X[j][Reorder_[Indices[k]]];
        }
      }
    }
    else {
      // transpose here
      for (int j = 0 ; j < NumVectors ; ++j) {
        for (int k = 0 ; k < Nnz ; ++k) {
          if (Reorder_[i] >= 0)
            Y[j][Reorder_[Indices[k]]] += Values[k] * X[j][i];
        }
      }
    }
  }

  return(0);
}

//==============================================================================
int Ifpack_SingletonFilter::
Solve(bool /* Upper */, bool /* Trans */, bool /* UnitDiagonal */,
      const Epetra_MultiVector& /* X */, Epetra_MultiVector& /* Y */) const
{
  return(-1);
}

//==============================================================================
int Ifpack_SingletonFilter::
Apply(const Epetra_MultiVector& X, Epetra_MultiVector& Y) const
{
  IFPACK_CHK_ERR(Multiply(false,X,Y));
  return(0);
}

//==============================================================================
int Ifpack_SingletonFilter::
ApplyInverse(const Epetra_MultiVector& /* X */, Epetra_MultiVector& /* Y */) const
{
  return(-1); // NOT IMPLEMENTED AT THIS STAGE
}

//==============================================================================
int Ifpack_SingletonFilter::
SolveSingletons(const Epetra_MultiVector& RHS,
                Epetra_MultiVector& LHS)
{
  for (int i = 0 ; i < NumSingletons_ ; ++i) {
    int ii = SingletonIndex_[i];
    // get the diagonal value for the singleton
    int Nnz;
    A_->ExtractMyRowCopy(ii,MaxNumEntriesA_,Nnz,
                        &Values_[0], &Indices_[0]);
    for (int j = 0 ; j < Nnz ; ++j) {
      if (Indices_[j] == ii) {
        for (int k = 0 ; k < LHS.NumVectors() ; ++k)
          LHS[k][ii] = RHS[k][ii] / Values_[j];
      }
    }
  }

  return(0);
}

//==============================================================================
int Ifpack_SingletonFilter::
CreateReducedRHS(const Epetra_MultiVector& LHS,
                 const Epetra_MultiVector& RHS,
                 Epetra_MultiVector& ReducedRHS)
{
  int NumVectors = LHS.NumVectors();

  for (int i = 0 ; i < NumRows_ ; ++i)
    for (int k = 0 ; k < NumVectors ; ++k)
      ReducedRHS[k][i] = RHS[k][InvReorder_[i]];

  for (int i = 0 ; i < NumRows_ ; ++i) {
    int ii = InvReorder_[i];
    int Nnz;
    IFPACK_CHK_ERR(A_->ExtractMyRowCopy(ii,MaxNumEntriesA_,Nnz,
                                        &Values_[0], &Indices_[0]));

    for (int j = 0 ; j < Nnz ; ++j) {
      if (Reorder_[Indices_[j]] == -1) {
        for (int k = 0 ; k < NumVectors ; ++k)
          ReducedRHS[k][i] -= Values_[j] * LHS[k][Indices_[j]];
      }
    }
  }
  return(0);
}

//==============================================================================
int Ifpack_SingletonFilter::
UpdateLHS(const Epetra_MultiVector& ReducedLHS,
          Epetra_MultiVector& LHS)
{
  for (int i = 0 ; i < NumRows_ ; ++i)
    for (int k = 0 ; k < LHS.NumVectors() ; ++k)
      LHS[k][InvReorder_[i]] = ReducedLHS[k][i];

  return(0);
}