2: static char help[] = "Tests MatGetSubmatrix() in parallel.";

  4: #include <petscmat.h>

  8: int main(int argc,char **args)
  9: {
 10:   Mat            C,A;
 11:   PetscInt       i,j,m = 3,n = 2,rstart,rend;
 12:   PetscMPIInt    size,rank;
 14:   PetscScalar    v;
 15:   IS             isrow,iscol;
 16:   PetscBool      flg;
 17:   char           type[256];

 19:   PetscInitialize(&argc,&args,(char*)0,help);
 20:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
 21:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 22:   n    = 2*size;

 24:   PetscStrcpy(type,MATSAME);
 25:   PetscOptionsGetString(NULL,"-mat_type",type,256,NULL);

 27:   PetscStrcmp(type,MATMPIDENSE,&flg);
 28:   if (flg) {
 29:     MatCreateDense(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE, m*n,m*n,NULL,&C);
 30:   } else {
 31:     MatCreateAIJ(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE, m*n,m*n,PETSC_DECIDE,NULL,PETSC_DECIDE,NULL,&C);
 32:   }

 34:   /*
 35:         This is JUST to generate a nice test matrix, all processors fill up
 36:     the entire matrix. This is not something one would ever do in practice.
 37:   */
 38:   for (i=0; i<m*n; i++) {
 39:     for (j=0; j<m*n; j++) {
 40:       v    = i + j + 1;
 41:       MatSetValues(C,1,&i,1,&j,&v,INSERT_VALUES);
 42:     }
 43:   }
 44:   MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
 45:   MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);
 46:   PetscViewerSetFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_COMMON);
 47:   MatView(C,PETSC_VIEWER_STDOUT_WORLD);

 49:   /*
 50:      Generate a new matrix consisting of every second row and column of
 51:    the original matrix
 52:   */
 53:   MatGetOwnershipRange(C,&rstart,&rend);
 54:   /* Create parallel IS with the rows we want on THIS processor */
 55:   ISCreateStride(PETSC_COMM_WORLD,(rend-rstart)/2,rstart,2,&isrow);
 56:   /* Create parallel IS with the rows we want on THIS processor (same as rows for now) */
 57:   ISCreateStride(PETSC_COMM_WORLD,(rend-rstart)/2,rstart,2,&iscol);
 58:   MatGetSubMatrix(C,isrow,iscol,MAT_INITIAL_MATRIX,&A);
 59:   MatView(A,PETSC_VIEWER_STDOUT_WORLD);

 61:   MatGetSubMatrix(C,isrow,iscol,MAT_REUSE_MATRIX,&A);
 62:   MatView(A,PETSC_VIEWER_STDOUT_WORLD);

 64:   ISDestroy(&isrow);
 65:   ISDestroy(&iscol);
 66:   MatDestroy(&A);
 67:   MatDestroy(&C);
 68:   PetscFinalize();
 69:   return 0;
 70: }