Date: 2022-03-04T17:38:16+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: /*T
      4:    Concepts: Mat^mat partitioning
      5:    Concepts: Mat^image segmentation
      6:    Processors: n
      7: T*/

      9: #include <petscmat.h>

     11: int main(int argc, char **args)
     12: {
     13:   Mat             A;
     14:   MatPartitioning part;
     15:   IS              is;
     16:   PetscInt        i,m,N,rstart,rend,nemptyranks,*emptyranks,nbigranks,*bigranks;
     17:   PetscMPIInt     rank,size;
     18:   PetscErrorCode  ierr;

     20:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
     21:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
     22:   MPI_Comm_size(PETSC_COMM_WORLD,&size);

     24:   nemptyranks = 10;
     25:   nbigranks   = 10;
     26:   PetscMalloc2(nemptyranks,&emptyranks,nbigranks,&bigranks);

     28:   PetscOptionsBegin(PETSC_COMM_WORLD,NULL,"Partitioning example options",NULL);
     29:   PetscOptionsIntArray("-emptyranks","Ranks to be skipped by partition","",emptyranks,&nemptyranks,NULL);
     30:   PetscOptionsIntArray("-bigranks","Ranks to be overloaded","",bigranks,&nbigranks,NULL);
     31:   PetscOptionsEnd();

     33:   m = 1;
     34:   for (i=0; i<nemptyranks; i++) if (rank == emptyranks[i]) m = 0;
     35:   for (i=0; i<nbigranks; i++) if (rank == bigranks[i]) m = 5;

     37:   MatCreate(PETSC_COMM_WORLD,&A);
     38:   MatSetSizes(A,m,m,PETSC_DECIDE,PETSC_DECIDE);
     39:   MatSetFromOptions(A);
     40:   MatSeqAIJSetPreallocation(A,3,NULL);
     41:   MatMPIAIJSetPreallocation(A,3,NULL,2,NULL);
     42:   MatSeqBAIJSetPreallocation(A,1,3,NULL);
     43:   MatMPIBAIJSetPreallocation(A,1,3,NULL,2,NULL);
     44:   MatSeqSBAIJSetPreallocation(A,1,2,NULL);
     45:   MatMPISBAIJSetPreallocation(A,1,2,NULL,1,NULL);

     47:   MatGetSize(A,NULL,&N);
     48:   MatGetOwnershipRange(A,&rstart,&rend);
     49:   for (i=rstart; i<rend; i++) {
     50:     const PetscInt    cols[] = {(i+N-1)%N,i,(i+1)%N};
     51:     const PetscScalar vals[] = {1,1,1};
     52:     MatSetValues(A,1,&i,3,cols,vals,INSERT_VALUES);
     53:   }
     54:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
     55:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
     56:   MatView(A,PETSC_VIEWER_STDOUT_WORLD);

     58:   MatPartitioningCreate(PETSC_COMM_WORLD,&part);
     59:   MatPartitioningSetAdjacency(part,A);
     60:   MatPartitioningSetFromOptions(part);
     61:   MatPartitioningApply(part,&is);
     62:   ISView(is,PETSC_VIEWER_STDOUT_WORLD);
     63:   ISDestroy(&is);
     64:   MatPartitioningDestroy(&part);
     65:   MatDestroy(&A);
     66:   PetscFree2(emptyranks,bigranks);
     67:   PetscFinalize();
     68:   return ierr;
     69: }

     71: /*TEST

     73:    test:
     74:       nsize: 8
     75:       args: -emptyranks 0,2,4 -bigranks 1,3,7 -mat_partitioning_type average
     76:       # cannot test with external package partitioners since they produce different results on different systems

     78: TEST*/