Date: 2026-03-31T05:46:26+00:00

Actual source code: ex17.c

      1: static char help[] = "Example of using graph partitioning with a matrix in which some procs have empty ownership\n\n";

      3: #include <petscmat.h>

      5: int main(int argc, char **args)
      6: {
      7:   Mat             A;
      8:   MatPartitioning part;
      9:   IS              is;
     10:   PetscInt        i, m, N, rstart, rend, nemptyranks, *emptyranks, nbigranks, *bigranks;
     11:   PetscMPIInt     rank, size;

     13:   PetscFunctionBeginUser;
     14:   PetscCall(PetscInitialize(&argc, &args, NULL, help));
     15:   PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
     16:   PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));

     18:   nemptyranks = 10;
     19:   nbigranks   = 10;
     20:   PetscCall(PetscMalloc2(nemptyranks, &emptyranks, nbigranks, &bigranks));

     22:   PetscOptionsBegin(PETSC_COMM_WORLD, NULL, "Partitioning example options", NULL);
     23:   PetscCall(PetscOptionsIntArray("-emptyranks", "Ranks to be skipped by partition", "", emptyranks, &nemptyranks, NULL));
     24:   PetscCall(PetscOptionsIntArray("-bigranks", "Ranks to be overloaded", "", bigranks, &nbigranks, NULL));
     25:   PetscOptionsEnd();

     27:   m = 1;
     28:   for (i = 0; i < nemptyranks; i++)
     29:     if (rank == emptyranks[i]) m = 0;
     30:   for (i = 0; i < nbigranks; i++)
     31:     if (rank == bigranks[i]) m = 5;

     33:   PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
     34:   PetscCall(MatSetSizes(A, m, m, PETSC_DECIDE, PETSC_DECIDE));
     35:   PetscCall(MatSetFromOptions(A));
     36:   PetscCall(MatSeqAIJSetPreallocation(A, 3, NULL));
     37:   PetscCall(MatMPIAIJSetPreallocation(A, 3, NULL, 2, NULL));
     38:   PetscCall(MatSeqBAIJSetPreallocation(A, 1, 3, NULL));
     39:   PetscCall(MatMPIBAIJSetPreallocation(A, 1, 3, NULL, 2, NULL));
     40:   PetscCall(MatSeqSBAIJSetPreallocation(A, 1, 2, NULL));
     41:   PetscCall(MatMPISBAIJSetPreallocation(A, 1, 2, NULL, 1, NULL));

     43:   PetscCall(MatGetSize(A, NULL, &N));
     44:   PetscCall(MatGetOwnershipRange(A, &rstart, &rend));
     45:   for (i = rstart; i < rend; i++) {
     46:     const PetscInt    cols[] = {(i + N - 1) % N, i, (i + 1) % N};
     47:     const PetscScalar vals[] = {1, 1, 1};
     48:     PetscCall(MatSetValues(A, 1, &i, 3, cols, vals, INSERT_VALUES));
     49:   }
     50:   PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
     51:   PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
     52:   PetscCall(MatView(A, PETSC_VIEWER_STDOUT_WORLD));

     54:   PetscCall(MatPartitioningCreate(PETSC_COMM_WORLD, &part));
     55:   PetscCall(MatPartitioningSetAdjacency(part, A));
     56:   PetscCall(MatPartitioningSetFromOptions(part));
     57:   PetscCall(MatPartitioningApply(part, &is));
     58:   PetscCall(ISView(is, PETSC_VIEWER_STDOUT_WORLD));
     59:   PetscCall(ISDestroy(&is));
     60:   PetscCall(MatPartitioningDestroy(&part));
     61:   PetscCall(MatDestroy(&A));
     62:   PetscCall(PetscFree2(emptyranks, bigranks));
     63:   PetscCall(PetscFinalize());
     64:   return 0;
     65: }

     67: /*TEST

     69:    test:
     70:       nsize: 8
     71:       args: -emptyranks 0,2,4 -bigranks 1,3,7 -mat_partitioning_type average
     72:       # cannot test with external package partitioners since they produce different results on different systems

     74: TEST*/