# [Trilinos-Users] Problem with EpetraExt::MatrixMatrix::Multiply

bender calculon calculondonbot777 at hotmail.com
Sun Sep 20 04:32:22 MDT 2009

```Hi,

I have this problem with EpetraExt:MatrixMatrix::Multiply. I
want to multiply two Epetra_CrsMatrix get from
Trilinos_Util::CrsMatrixGallery.
If I multiply two full matrix ( for
example Hilber Matrix, Cauchy matrix or kms matrix ) or two diagonal
matrix I obtain a correct result, but if I multiply two sparse matrix i
obtain an absurd result.

I explain my problem with a part of my code:

Trilinos_Util::CrsMatrixGallery Problem(problem, Comm);   // problem = "laplace_2d"
Problem.Set("problem_size",size);                               // size = 4
Problem.Set("map_type","linear");
Num_Glob = read_A->Map().NumGlobalElements();    // int Num_Glob
Epetra_Map Map_func(Num_Glob,0,Comm);
Epetra_Export exporter(read_A -> Map(), Map_func);     // I want to export  data from *read_A to matrix_A
Epetra_CrsMatrix Matrix_A(Copy, Map_func, 0);
Matrix_A.FillComplete();
cout << Matrix_A;
Epetra_CrsMatrix Matrix_C(Matrix_A);                             // copy of Matrix_A;
Matrix_C.PutScalar(0);
Matrix_C.FillComplete();

EpetraExt::MatrixMatrix::Multiply(Matrix_A,false,Matrix_A,false,Matrix_C);
// This operation make Matrix_C = Matrix_A*Matrix_A +C not C = A*A

If i put problem = "laplace_2d" and "problem_size" = 4 I obtain this result:

./ex2.exe -problem laplace_2d -size 4
Epetra::CrsMatrix

Number of Global Rows        = 4
Number of Global Cols        = 4
Number of Global Diagonals   = 4
Number of Global Nonzeros    = 12
Global Maximum Num Entries   = 3

Number of My Rows        = 4
Number of My Cols        = 4
Number of My Diagonals   = 4
Number of My Nonzeros    = 12
My Maximum Num Entries   = 3

Processor    Row Index    Col Index           Value
0             0             0                      17
0             0             1                      -8
0             0             2                      -4
0             1             0                       0
0             1             1                       0
0             1             3                       0
0             2             0                       0
0             2             2                       0
0             2             3                       0
0             3             1                       0
0             3             2                       0
0             3             3                       0

and you can see that is not correct.

I have trilinos release 9.0.

T

Best regards

Maurizio
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