1: #include <../src/mat/impls/aij/mpi/mpiaij.h>

  3: PetscErrorCode  MatGetMultiProcBlock_MPIAIJ(Mat mat, MPI_Comm subComm, MatReuse scall,Mat *subMat)
  4: {
  6:   Mat_MPIAIJ     *aij  = (Mat_MPIAIJ*)mat->data;
  7:   Mat_SeqAIJ     *aijB = (Mat_SeqAIJ*)aij->B->data;
  8:   PetscMPIInt    subCommSize,subCommRank;
  9:   PetscMPIInt    *commRankMap,subRank,rank,commRank;
 10:   PetscInt       *garrayCMap,col,i,j,*nnz,newRow,newCol;

 13:   MPI_Comm_size(subComm,&subCommSize);
 14:   MPI_Comm_rank(subComm,&subCommRank);
 15:   MPI_Comm_rank(PetscObjectComm((PetscObject)mat),&commRank);

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

 24:     /* need to setup rmap and cmap before Preallocation */
 25:     PetscLayoutSetUp((*subMat)->rmap);
 26:     PetscLayoutSetUp((*subMat)->cmap);
 27:   }

 29:   /* create a map of comm_rank from subComm to comm - should commRankMap and garrayCMap be kept for reused? */
 30:   PetscMalloc1(subCommSize,&commRankMap);
 31:   MPI_Allgather(&commRank,1,MPI_INT,commRankMap,1,MPI_INT,subComm);

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

 48:   if (scall == MAT_INITIAL_MATRIX) {
 49:     /* Compute preallocation for the offdiag mat */
 50:     PetscCalloc1(aij->B->rmap->n,&nnz);
 51:     for (i=0; i<aij->B->rmap->n; i++) {
 52:       for (j=aijB->i[i]; j<aijB->i[i+1]; j++) {
 53:         if (garrayCMap[aijB->j[j]]) nnz[i]++;
 54:       }
 55:     }
 56:     MatMPIAIJSetPreallocation(*(subMat),0,NULL,0,nnz);

 58:     /* reuse diag block with the new submat */
 59:     MatDestroy(&((Mat_MPIAIJ*)((*subMat)->data))->A);
 60:     ((Mat_MPIAIJ*)((*subMat)->data))->A = aij->A;
 61:     PetscObjectReference((PetscObject)aij->A);
 62:   } else if (((Mat_MPIAIJ*)(*subMat)->data)->A != aij->A) {
 63:     PetscObject obj = (PetscObject)((Mat_MPIAIJ*)((*subMat)->data))->A;
 64:     PetscObjectReference((PetscObject)obj);
 65:     ((Mat_MPIAIJ*)((*subMat)->data))->A = aij->A;
 66:     PetscObjectReference((PetscObject)aij->A);
 67:   }

 69:   /* Traverse aij->B and insert values into subMat */
 70:   if ((*subMat)->assembled) {
 71:     (*subMat)->was_assembled = PETSC_TRUE;
 72:     (*subMat)->assembled     = PETSC_FALSE;
 73:   }
 74:   for (i=0; i<aij->B->rmap->n; i++) {
 75:     newRow = (*subMat)->rmap->range[subCommRank] + i;
 76:     for (j=aijB->i[i]; j<aijB->i[i+1]; j++) {
 77:       newCol = garrayCMap[aijB->j[j]];
 78:       if (newCol) {
 79:         newCol--; /* remove the increment */
 80:         MatSetValues_MPIAIJ(*subMat,1,&newRow,1,&newCol,(aijB->a+j),INSERT_VALUES);
 81:       }
 82:     }
 83:   }
 84:   MatAssemblyBegin(*subMat,MAT_FINAL_ASSEMBLY);
 85:   MatAssemblyEnd(*subMat,MAT_FINAL_ASSEMBLY);

 87:   /* deallocate temporary data */
 88:   PetscFree(commRankMap);
 89:   PetscFree(garrayCMap);
 90:   if (scall == MAT_INITIAL_MATRIX) {
 91:     PetscFree(nnz);
 92:   }
 93:   return(0);
 94: }