Actual source code: ex35.c
petsc-3.4.2 2013-07-02

      2: static char help[] = "Tests MatGetSubMatrices().\n\n";

      4: #include <petscmat.h>

      8: int main(int argc,char **args)
      9: {
     10:   Mat            A,B,*Bsub;
     11:   PetscInt       i,j,m = 6,n = 6,N = 36,Ii,J;
     13:   PetscScalar    v;
     14:   IS             isrow;

     16:   PetscInitialize(&argc,&args,(char*)0,help);

     18:   MatCreateSeqAIJ(PETSC_COMM_WORLD,N,N,5,NULL,&A);
     19:   for (i=0; i<m; i++) {
     20:     for (j=0; j<n; j++) {
     21:       v = -1.0;  Ii = j + n*i;
     22:       if (i>0)   {J = Ii - n; MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);}
     23:       if (i<m-1) {J = Ii + n; MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);}
     24:       if (j>0)   {J = Ii - 1; MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);}
     25:       if (j<n-1) {J = Ii + 1; MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);}
     26:       v = 4.0; MatSetValues(A,1,&Ii,1,&Ii,&v,INSERT_VALUES);
     27:     }
     28:   }
     29:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
     30:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
     31:   MatView(A,PETSC_VIEWER_STDOUT_SELF);

     33:   /* take the first diagonal block */
     34:   ISCreateStride(PETSC_COMM_WORLD,m,0,1,&isrow);
     35:   MatGetSubMatrices(A,1,&isrow,&isrow,MAT_INITIAL_MATRIX,&Bsub);
     36:   B    = *Bsub;
     37:   PetscFree(Bsub);
     38:   ISDestroy(&isrow);
     39:   MatView(B,PETSC_VIEWER_STDOUT_SELF);
     40:   MatDestroy(&B);

     42:   /* take a strided block */
     43:   ISCreateStride(PETSC_COMM_WORLD,m,0,2,&isrow);
     44:   MatGetSubMatrices(A,1,&isrow,&isrow,MAT_INITIAL_MATRIX,&Bsub);
     45:   B    = *Bsub;
     46:   PetscFree(Bsub);
     47:   ISDestroy(&isrow);
     48:   MatView(B,PETSC_VIEWER_STDOUT_SELF);
     49:   MatDestroy(&B);

     51:   /* take the last block */
     52:   ISCreateStride(PETSC_COMM_WORLD,m,N-m-1,1,&isrow);
     53:   MatGetSubMatrices(A,1,&isrow,&isrow,MAT_INITIAL_MATRIX,&Bsub);
     54:   B    = *Bsub;
     55:   PetscFree(Bsub);
     56:   ISDestroy(&isrow);
     57:   MatView(B,PETSC_VIEWER_STDOUT_SELF);

     59:   MatDestroy(&B);
     60:   MatDestroy(&A);

     62:   PetscFinalize();
     63:   return 0;
     64: }