1: #include <../src/mat/impls/baij/mpi/mpibaij.h>

  3: PetscErrorCode MatGetMultiProcBlock_MPIBAIJ(Mat mat, MPI_Comm subComm, MatReuse scall, Mat *subMat)
  4: {
  5:   Mat_MPIBAIJ *aij  = (Mat_MPIBAIJ *)mat->data;
  6:   Mat_SeqBAIJ *aijB = (Mat_SeqBAIJ *)aij->B->data;
  7:   PetscMPIInt  commRank, subCommSize, subCommRank;
  8:   PetscMPIInt *commRankMap, subRank, rank, commsize;
  9:   PetscInt    *garrayCMap, col, i, j, *nnz, newRow, newCol, *newbRow, *newbCol, k, k1;
 10:   PetscInt     bs = mat->rmap->bs;
 11:   PetscScalar *vals, *aijBvals;

 13:   PetscFunctionBegin;
 14:   PetscCallMPI(MPI_Comm_size(PetscObjectComm((PetscObject)mat), &commsize));
 15:   PetscCallMPI(MPI_Comm_size(subComm, &subCommSize));

 17:   /* create subMat object with the relevant layout */
 18:   if (scall == MAT_INITIAL_MATRIX) {
 19:     PetscCall(MatCreate(subComm, subMat));
 20:     PetscCall(MatSetType(*subMat, MATMPIBAIJ));
 21:     PetscCall(MatSetSizes(*subMat, mat->rmap->n, mat->cmap->n, PETSC_DECIDE, PETSC_DECIDE));
 22:     PetscCall(MatSetBlockSizes(*subMat, mat->rmap->bs, mat->cmap->bs));

 24:     /* need to setup rmap and cmap before Preallocation */
 25:     PetscCall(PetscLayoutSetBlockSize((*subMat)->rmap, mat->rmap->bs));
 26:     PetscCall(PetscLayoutSetBlockSize((*subMat)->cmap, mat->cmap->bs));
 27:     PetscCall(PetscLayoutSetUp((*subMat)->rmap));
 28:     PetscCall(PetscLayoutSetUp((*subMat)->cmap));
 29:   }

 31:   /* create a map of comm_rank from subComm to comm - should commRankMap and garrayCMap be kept for reused? */
 32:   PetscCallMPI(MPI_Comm_rank(PetscObjectComm((PetscObject)mat), &commRank));
 33:   PetscCallMPI(MPI_Comm_rank(subComm, &subCommRank));
 34:   PetscCall(PetscMalloc1(subCommSize, &commRankMap));
 35:   PetscCallMPI(MPI_Allgather(&commRank, 1, MPI_INT, commRankMap, 1, MPI_INT, subComm));

 37:   /* Traverse garray and identify blocked column indices [of offdiag mat] that
 38:    should be discarded. For the ones not discarded, store the newCol+1
 39:    value in garrayCMap */
 40:   PetscCall(PetscCalloc1(aij->B->cmap->n / bs, &garrayCMap));
 41:   for (i = 0; i < aij->B->cmap->n / bs; i++) {
 42:     col = aij->garray[i]; /* blocked column index */
 43:     for (subRank = 0; subRank < subCommSize; subRank++) {
 44:       rank = commRankMap[subRank];
 45:       if ((col >= mat->cmap->range[rank] / bs) && (col < mat->cmap->range[rank + 1] / bs)) {
 46:         garrayCMap[i] = (((*subMat)->cmap->range[subRank] - mat->cmap->range[rank]) / bs + col + 1);
 47:         break;
 48:       }
 49:     }
 50:   }

 52:   if (scall == MAT_INITIAL_MATRIX) {
 53:     /* Now compute preallocation for the offdiag mat */
 54:     PetscCall(PetscCalloc1(aij->B->rmap->n / bs, &nnz));
 55:     for (i = 0; i < aij->B->rmap->n / bs; i++) {
 56:       for (j = aijB->i[i]; j < aijB->i[i + 1]; j++) {
 57:         if (garrayCMap[aijB->j[j]]) nnz[i]++;
 58:       }
 59:     }
 60:     PetscCall(MatMPIBAIJSetPreallocation(*(subMat), bs, 0, NULL, 0, nnz));

 62:     /* reuse diag block with the new submat */
 63:     PetscCall(MatDestroy(&((Mat_MPIBAIJ *)((*subMat)->data))->A));

 65:     ((Mat_MPIBAIJ *)((*subMat)->data))->A = aij->A;

 67:     PetscCall(PetscObjectReference((PetscObject)aij->A));
 68:   } else if (((Mat_MPIBAIJ *)(*subMat)->data)->A != aij->A) {
 69:     PetscObject obj = (PetscObject)((Mat_MPIBAIJ *)((*subMat)->data))->A;

 71:     PetscCall(PetscObjectReference((PetscObject)obj));

 73:     ((Mat_MPIBAIJ *)((*subMat)->data))->A = aij->A;

 75:     PetscCall(PetscObjectReference((PetscObject)aij->A));
 76:   }

 78:   /* Now traverse aij->B and insert values into subMat */
 79:   PetscCall(PetscMalloc3(bs, &newbRow, bs, &newbCol, bs * bs, &vals));
 80:   for (i = 0; i < aij->B->rmap->n / bs; i++) {
 81:     newRow = (*subMat)->rmap->range[subCommRank] + i * bs;
 82:     for (j = aijB->i[i]; j < aijB->i[i + 1]; j++) {
 83:       newCol = garrayCMap[aijB->j[j]];
 84:       if (newCol) {
 85:         newCol--; /* remove the increment */
 86:         newCol *= bs;
 87:         for (k = 0; k < bs; k++) {
 88:           newbRow[k] = newRow + k;
 89:           newbCol[k] = newCol + k;
 90:         }
 91:         /* copy column-oriented aijB->a into row-oriented vals */
 92:         aijBvals = aijB->a + j * bs * bs;
 93:         for (k1 = 0; k1 < bs; k1++) {
 94:           for (k = 0; k < bs; k++) vals[k1 + k * bs] = *aijBvals++;
 95:         }
 96:         PetscCall(MatSetValues(*subMat, bs, newbRow, bs, newbCol, vals, INSERT_VALUES));
 97:       }
 98:     }
 99:   }
100:   PetscCall(MatAssemblyBegin(*subMat, MAT_FINAL_ASSEMBLY));
101:   PetscCall(MatAssemblyEnd(*subMat, MAT_FINAL_ASSEMBLY));

103:   /* deallocate temporary data */
104:   PetscCall(PetscFree3(newbRow, newbCol, vals));
105:   PetscCall(PetscFree(commRankMap));
106:   PetscCall(PetscFree(garrayCMap));
107:   if (scall == MAT_INITIAL_MATRIX) PetscCall(PetscFree(nnz));
108:   PetscFunctionReturn(PETSC_SUCCESS);
109: }