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: }