xref: /petsc/src/mat/utils/zerorows.c (revision 31d78bcd2b98084dc1368b20eb1129c8b9fb39fe)

#include <petsc/private/matimpl.h>
#include <petscsf.h>

/* this function maps rows to locally owned rows */
PETSC_INTERN PetscErrorCode MatZeroRowsMapLocal_Private(Mat A, PetscInt N, const PetscInt *rows, PetscInt *nr, PetscInt **olrows)
{
  PetscInt    *owners = A->rmap->range;
  PetscInt     n      = A->rmap->n;
  PetscSF      sf;
  PetscInt    *lrows;
  PetscSFNode *rrows;
  PetscMPIInt  rank, p = 0;
  PetscInt     r, len  = 0;

  PetscFunctionBegin;
  /* Create SF where leaves are input rows and roots are owned rows */
  PetscCallMPI(MPI_Comm_rank(PetscObjectComm((PetscObject)A), &rank));
  PetscCall(PetscMalloc1(n, &lrows));
  for (r = 0; r < n; ++r) lrows[r] = -1;
  if (!A->nooffproczerorows) PetscCall(PetscMalloc1(N, &rrows));
  for (r = 0; r < N; ++r) {
    const PetscInt idx = rows[r];
    PetscCheck(idx >= 0 && A->rmap->N > idx, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Row %" PetscInt_FMT " out of range [0,%" PetscInt_FMT ")", idx, A->rmap->N);
    if (idx < owners[p] || owners[p + 1] <= idx) { /* short-circuit the search if the last p owns this row too */
      PetscCall(PetscLayoutFindOwner(A->rmap, idx, &p));
    }
    if (A->nooffproczerorows) {
      PetscCheck(p == rank, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "MAT_NO_OFF_PROC_ZERO_ROWS set, but row %" PetscInt_FMT " is not owned by rank %d", idx, rank);
      lrows[len++] = idx - owners[p];
    } else {
      rrows[r].rank  = p;
      rrows[r].index = rows[r] - owners[p];
    }
  }
  if (!A->nooffproczerorows) {
    PetscCall(PetscSFCreate(PetscObjectComm((PetscObject)A), &sf));
    PetscCall(PetscSFSetGraph(sf, n, N, NULL, PETSC_OWN_POINTER, rrows, PETSC_OWN_POINTER));
    /* Collect flags for rows to be zeroed */
    PetscCall(PetscSFReduceBegin(sf, MPIU_INT, (PetscInt *)rows, lrows, MPI_LOR));
    PetscCall(PetscSFReduceEnd(sf, MPIU_INT, (PetscInt *)rows, lrows, MPI_LOR));
    PetscCall(PetscSFDestroy(&sf));
    /* Compress and put in row numbers */
    for (r = 0; r < n; ++r)
      if (lrows[r] >= 0) lrows[len++] = r;
  }
  if (nr) *nr = len;
  if (olrows) *olrows = lrows;
  PetscFunctionReturn(PETSC_SUCCESS);
}