Actual source code: ex59.c
petsc-3.4.2 2013-07-02

      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: }