Actual source code: mpb_aij.c
petsc-3.10.5 2019-03-28
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      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    commRank,subCommSize,subCommRank;
      9:   PetscMPIInt    *commRankMap,subRank,rank,commsize;
     10:   PetscInt       *garrayCMap,col,i,j,*nnz,newRow,newCol;

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

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

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

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

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

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

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

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

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

     68:     PetscObjectReference((PetscObject)obj);

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

     72:     PetscObjectReference((PetscObject)aij->A);
     73:   }

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

     87:   /* assemble the submat */
     88:   MatAssemblyBegin(*subMat,MAT_FINAL_ASSEMBLY);
     89:   MatAssemblyEnd(*subMat,MAT_FINAL_ASSEMBLY);

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