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

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

 15:   MPI_Comm_size(PetscObjectComm((PetscObject)mat),&commsize);
 16:   MPI_Comm_size(subComm,&subCommSize);

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

 25:     /* need to setup rmap and cmap before Preallocation */
 26:     PetscLayoutSetUp((*subMat)->rmap);
 27:     PetscLayoutSetUp((*subMat)->cmap);
 28:   }

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

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

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

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

 64:     ((Mat_MPIAIJ*)((*subMat)->data))->A = aij->A;

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

 70:     PetscObjectReference((PetscObject)obj);

 72:     ((Mat_MPIAIJ*)((*subMat)->data))->A = aij->A;

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

 77:   /* Now traverse aij->B and insert values into subMat */
 78:   for (i=0; i<aij->B->rmap->n; i++) {
 79:     newRow = (*subMat)->rmap->range[subCommRank] + i;
 80:     for (j=aijB->i[i]; j<aijB->i[i+1]; j++) {
 81:       newCol = garrayCMap[aijB->j[j]];
 82:       if (newCol) {
 83:         newCol--; /* remove the increment */
 84:         MatSetValues(*subMat,1,&newRow,1,&newCol,(aijB->a+j),INSERT_VALUES);
 85:       }
 86:     }
 87:   }

 89:   /* assemble the submat */
 90:   MatAssemblyBegin(*subMat,MAT_FINAL_ASSEMBLY);
 91:   MatAssemblyEnd(*subMat,MAT_FINAL_ASSEMBLY);

 93:   /* deallocate temporary data */
 94:   PetscFree(commRankMap);
 95:   PetscFree(garrayCMap);
 96:   if (scall == MAT_INITIAL_MATRIX) {
 97:     PetscFree(nnz);
 98:   }
 99:   return(0);
100: }