Ifpack_SparsityFilter.cpp

00001 /*@HEADER
00002 // ***********************************************************************
00003 //
00004 //       Ifpack: Object-Oriented Algebraic Preconditioner Package
00005 //                 Copyright (2002) Sandia Corporation
00006 //
00007 // Under terms of Contract DE-AC04-94AL85000, there is a non-exclusive
00008 // license for use of this work by or on behalf of the U.S. Government.
00009 //
00010 // This library is free software; you can redistribute it and/or modify
00011 // it under the terms of the GNU Lesser General Public License as
00012 // published by the Free Software Foundation; either version 2.1 of the
00013 // License, or (at your option) any later version.
00014 //
00015 // This library is distributed in the hope that it will be useful, but
00016 // WITHOUT ANY WARRANTY; without even the implied warranty of
00017 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00018 // Lesser General Public License for more details.
00019 //
00020 // You should have received a copy of the GNU Lesser General Public
00021 // License along with this library; if not, write to the Free Software
00022 // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
00023 // USA
00024 // Questions? Contact Michael A. Heroux (maherou@sandia.gov)
00025 //
00026 // ***********************************************************************
00027 //@HEADER
00028 */
00029 
00030 #include "Ifpack_ConfigDefs.h"
00031 #include "Ifpack_SparsityFilter.h"
00032 #include "Epetra_ConfigDefs.h"
00033 #include "Epetra_RowMatrix.h"
00034 #include "Epetra_Comm.h"
00035 #include "Epetra_Map.h"
00036 #include "Epetra_MultiVector.h"
00037 #include "Epetra_Vector.h"
00038 
00039 //==============================================================================
00040 Ifpack_SparsityFilter::Ifpack_SparsityFilter(const Teuchos::RefCountPtr<Epetra_RowMatrix>& Matrix,
00041                          int AllowedEntries, 
00042                          int AllowedBandwidth) :
00043   A_(Matrix),
00044   MaxNumEntries_(0),
00045   MaxNumEntriesA_(0),
00046   AllowedBandwidth_(AllowedBandwidth),
00047   AllowedEntries_(AllowedEntries),
00048   NumNonzeros_(0),
00049   NumRows_(0)
00050 {
00051   // use this filter only on serial matrices
00052   if (A_->Comm().NumProc() != 1) {
00053     cerr << "Ifpack_SparsityFilter can be used with Comm().NumProc() == 1" << endl;
00054     cerr << "only. This class is a tool for Ifpack_AdditiveSchwarz," << endl;
00055     cerr << "and it is not meant to be used otherwise." << endl;
00056     exit(EXIT_FAILURE);
00057   }
00058 
00059   // only square serial matrices
00060   if ((A_->NumMyRows() != A_->NumMyCols()) ||
00061      (A_->NumMyRows() != A_->NumGlobalRows()))
00062     IFPACK_CHK_ERRV(-1);
00063 
00064   NumRows_ = A_->NumMyRows();
00065   MaxNumEntriesA_ = A_->MaxNumEntries();
00066   Indices_.resize(MaxNumEntriesA_);
00067   Values_.resize(MaxNumEntriesA_);
00068 
00069   // default value is to not consider bandwidth
00070   if (AllowedBandwidth_ == -1)
00071     AllowedBandwidth_ = NumRows_;
00072   
00073   // computes the number of nonzero elements per row in the 
00074   // dropped matrix. Stores this number in NumEntries_.
00075   // Also, computes the global number of nonzeros.
00076   vector<int>    Ind(MaxNumEntriesA_);
00077   vector<double> Val(MaxNumEntriesA_);
00078 
00079   NumEntries_.resize(NumRows_);
00080   for (int i = 0 ; i < NumRows_ ; ++i)
00081     NumEntries_[i] = MaxNumEntriesA_;
00082 
00083   for (int i = 0 ; i < A_->NumMyRows() ; ++i) {
00084     int Nnz;
00085     IFPACK_CHK_ERRV(ExtractMyRowCopy(i,MaxNumEntriesA_,Nnz,
00086                      &Val[0], &Ind[0]));
00087 
00088     NumEntries_[i] = Nnz;
00089     NumNonzeros_ += Nnz;
00090     if (Nnz > MaxNumEntries_)
00091       MaxNumEntries_ = Nnz;
00092 
00093   }
00094 }
00095 
00096 //==============================================================================
00097 int Ifpack_SparsityFilter::
00098 ExtractMyRowCopy(int MyRow, int Length, int & NumEntries, 
00099          double *Values, int * Indices) const
00100 {
00101   if (Length < NumEntries_[MyRow])
00102     IFPACK_CHK_ERR(-1);
00103 
00104   int Nnz;
00105   IFPACK_CHK_ERR(A_->ExtractMyRowCopy(MyRow,MaxNumEntriesA_,Nnz,
00106                      &Values_[0],&Indices_[0]));
00107 
00108   double Threshold = 0.0;
00109     
00110   // this `if' is to define the cut-off value
00111   if (Nnz > AllowedEntries_) {
00112  
00113     vector<double> Values2(Nnz);
00114     int count = 0;
00115     for (int i = 0 ; i < Nnz ; ++i) {
00116       // skip diagonal entry (which is always inserted)
00117       if (Indices_[i] == MyRow)
00118     continue;
00119       // put absolute value
00120       Values2[count] = IFPACK_ABS(Values_[i]);
00121       count++;
00122     }
00123 
00124     for (int i = count ; i < Nnz ; ++i)
00125       Values2[i] = 0.0;
00126 
00127     // sort in descending order
00128     sort(Values2.rbegin(),Values2.rend());
00129     // get the cut-off value
00130     Threshold = Values2[AllowedEntries_ - 1];
00131 
00132   }
00133 
00134   // loop over all nonzero elements of row MyRow,
00135   // and drop elements below specified threshold.
00136   // Also, add value to zero diagonal
00137   NumEntries = 0;
00138 
00139   for (int i = 0 ; i < Nnz ; ++i) {
00140 
00141     if (IFPACK_ABS(Indices_[i] - MyRow) > AllowedBandwidth_)
00142       continue;
00143 
00144     if ((Indices_[i] != MyRow) && (IFPACK_ABS(Values_[i]) < Threshold))
00145       continue;
00146 
00147     Values[NumEntries] = Values_[i];
00148     Indices[NumEntries] = Indices_[i];
00149 
00150     NumEntries++;
00151     if (NumEntries > AllowedEntries_)
00152       break;
00153   }
00154 
00155   return(0);
00156 }
00157 
00158 //==============================================================================
00159 int Ifpack_SparsityFilter::
00160 ExtractDiagonalCopy(Epetra_Vector & Diagonal) const
00161 {
00162   IFPACK_RETURN(A_->ExtractDiagonalCopy(Diagonal));
00163 }
00164 
00165 //==============================================================================
00166 int Ifpack_SparsityFilter::
00167 Multiply(bool TransA, const Epetra_MultiVector& X, 
00168      Epetra_MultiVector& Y) const
00169 {
00170 
00171   int NumVectors = X.NumVectors();
00172   if (NumVectors != Y.NumVectors())
00173     IFPACK_CHK_ERR(-1);
00174 
00175   Y.PutScalar(0.0);
00176 
00177   vector<int> Indices(MaxNumEntries_);
00178   vector<double> Values(MaxNumEntries_);
00179 
00180   for (int i = 0 ; i < A_->NumMyRows() ; ++i) {
00181 
00182     int Nnz;
00183     ExtractMyRowCopy(i,MaxNumEntries_,Nnz,
00184              &Values[0], &Indices[0]);
00185     if (!TransA) {
00186       // no transpose first
00187       for (int j = 0 ; j < NumVectors ; ++j) {
00188     for (int k = 0 ; k < Nnz ; ++k) {
00189       Y[j][i] += Values[k] * X[j][Indices[k]];
00190     }
00191       }
00192     }
00193     else {
00194       // transpose here
00195       for (int j = 0 ; j < NumVectors ; ++j) {
00196     for (int k = 0 ; k < Nnz ; ++k) {
00197       Y[j][Indices[k]] += Values[k] * X[j][i];
00198     }
00199       }
00200     }
00201   }
00202 
00203   return(0);
00204 }
00205 
00206 //==============================================================================
00207 int Ifpack_SparsityFilter::
00208 Solve(bool Upper, bool Trans, bool UnitDiagonal, 
00209       const Epetra_MultiVector& X, Epetra_MultiVector& Y) const
00210 {
00211   IFPACK_CHK_ERR(-98);
00212 }
00213 
00214 //==============================================================================
00215 int Ifpack_SparsityFilter::
00216 Apply(const Epetra_MultiVector& X, Epetra_MultiVector& Y) const
00217 {
00218   IFPACK_RETURN(Multiply(UseTranspose(),X,Y));
00219 }
00220 
00221 //==============================================================================
00222 int Ifpack_SparsityFilter::
00223 ApplyInverse(const Epetra_MultiVector& X, Epetra_MultiVector& Y) const
00224 {
00225   IFPACK_CHK_ERR(-98); 
00226 }

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