Actual source code: mpb_aij.c
petsc-3.15.0 2021-03-30
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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    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: }