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Ifpack_ex_Filtering.cpp
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4// Ifpack: Object-Oriented Algebraic Preconditioner Package
5// Copyright (2002) Sandia Corporation
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7// Under terms of Contract DE-AC04-94AL85000, there is a non-exclusive
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41
42#include "Ifpack_ConfigDefs.h"
43#ifdef HAVE_MPI
44#include "Epetra_MpiComm.h"
45#else
46#include "Epetra_SerialComm.h"
47#endif
48#include "Epetra_Map.h"
49#include "Epetra_CrsMatrix.h"
50#include "Ifpack_DropFilter.h"
53#include "Ifpack_Utils.h"
54#include "Teuchos_RefCountPtr.hpp"
55
56int main(int argc, char *argv[])
57{
58 using std::cerr;
59 using std::cout;
60 using std::endl;
61
62#ifdef HAVE_MPI
63 MPI_Init(&argc,&argv);
64 Epetra_MpiComm Comm( MPI_COMM_WORLD );
65#else
67#endif
68
69 if (Comm.NumProc() != 1) {
70 cerr << "This example must be run with one process only." << endl;
71 // exit with success not to break the test harness
72#ifdef HAVE_MPI
73 MPI_Finalize();
74#endif
75 exit(EXIT_SUCCESS);
76 }
77
78 int NumPoints = 5;
79#if !defined(EPETRA_NO_32BIT_GLOBAL_INDICES) || !defined(EPETRA_NO_64BIT_GLOBAL_INDICES)
80 Epetra_Map Map(NumPoints,0,Comm);
81#else
82 Epetra_Map Map;
83#endif
84
85 Teuchos::RefCountPtr<Epetra_CrsMatrix> Matrix = Teuchos::rcp( new Epetra_CrsMatrix(Copy,Map,0) );
86
87 std::vector<int> Indices(NumPoints);
88 std::vector<double> Values(NumPoints);
89 double Diag = 0.0;
90
91 for (int i = 0 ; i < NumPoints ; ++i) {
92 // add a diagonal
93 Matrix->InsertGlobalValues(i,1,&Diag,&i);
94
95 // add off-diagonals
96 int NumEntries = 0;
97 for (int j = i + 1 ; j < NumPoints ; ++j) {
98 Indices[NumEntries] = j;
99 Values[NumEntries] = 1.0 * (j - i);
100 ++NumEntries;
101 }
102#if !defined(EPETRA_NO_32BIT_GLOBAL_INDICES) || !defined(EPETRA_NO_64BIT_GLOBAL_INDICES)
103 Matrix->InsertGlobalValues(i,NumEntries,&Values[0],&Indices[0]);
104#endif
105 }
106 Matrix->FillComplete();
107
108 // ================================= //
109 // print sparsity of original matrix //
110 // ================================= //
111
112 cout << "Sparsity, non-dropped matrix" << endl;
114
115 // ====================================== //
116 // create a new matrix, dropping by value //
117 // ====================================== //
118 //
119 // drop all elements below 4.0. Only the upper-right element
120 // is maintained, plus all the diagonals that are not
121 // considering in dropping.
122 Ifpack_DropFilter DropA(Matrix,4.0);
123 assert (DropA.MaxNumEntries() == 2);
124
125 cout << "Sparsity, dropping by value" << endl;
127
128 // ========================================= //
129 // create a new matrix, dropping by sparsity //
130 // ========================================= //
131 //
132 // Mantain 2 off-diagonal elements.
133 Ifpack_SparsityFilter SparsityA(Matrix,2);
134
135 cout << "Sparsity, dropping by sparsity" << endl;
137 assert (SparsityA.MaxNumEntries() == 3);
138
139 // ======================================== //
140 // create new matrices, dropping singletons //
141 // ======================================== //
142 //
143 // If we apply this filter NumPoints - 1 times,
144 // we end up with a one-row matrix
145 Ifpack_SingletonFilter Filter1(Matrix);
146 Ifpack_SingletonFilter Filter2(Teuchos::rcp(&Filter1, false));
147 Ifpack_SingletonFilter Filter3(Teuchos::rcp(&Filter2, false));
148 Ifpack_SingletonFilter Filter4(Teuchos::rcp(&Filter3, false));
149
150 cout << "Sparsity, dropping singletons 4 times" << endl;
152 assert (Filter4.NumMyRows() == 1);
153
154#ifdef HAVE_MPI
155 MPI_Finalize();
156#endif
157 return(EXIT_SUCCESS);
158}
159
Copy
void Ifpack_PrintSparsity_Simple(const Epetra_RowMatrix &A)
int main(int argc, char *argv[])
int NumProc() const
Ifpack_DropFilter: Filter based on matrix entries.
virtual int MaxNumEntries() const
Returns the maximum number of entries.
Ifpack_SingletonFilter: Filter based on matrix entries.
virtual int NumMyRows() const
Ifpack_SparsityFilter: a class to drop based on sparsity.
virtual int MaxNumEntries() const