Actual source code: mpb_aij.c

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

  5: PetscErrorCode  MatGetMultiProcBlock_MPIAIJ(Mat mat, MPI_Comm subComm, 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(((PetscObject)mat)->comm,&commsize);
 16:   MPI_Comm_size(subComm,&subCommSize);

 18:   /* create subMat object with the relavent layout */
 19:   MatCreate(subComm,subMat);
 20:   MatSetType(*subMat,MATMPIAIJ);
 21:   MatSetSizes(*subMat,mat->rmap->n,mat->cmap->n,PETSC_DECIDE,PETSC_DECIDE);
 22:   /* need to setup rmap and cmap before Preallocation */
 23:   PetscLayoutSetBlockSize((*subMat)->rmap,mat->rmap->bs);
 24:   PetscLayoutSetBlockSize((*subMat)->cmap,mat->cmap->bs);
 25:   PetscLayoutSetUp((*subMat)->rmap);
 26:   PetscLayoutSetUp((*subMat)->cmap);

 28:   /* create a map of comm_rank from subComm to comm */
 29:   MPI_Comm_rank(((PetscObject)mat)->comm,&commRank);
 30:   MPI_Comm_rank(subComm,&subCommRank);
 31:   PetscMalloc(subCommSize*sizeof(PetscMPIInt),&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:   PetscMalloc(aij->B->cmap->n*sizeof(PetscInt),&garrayCMap);
 38:   PetscMemzero(garrayCMap,aij->B->cmap->n*sizeof(PetscInt));
 39:   for (i=0; i<aij->B->cmap->n; i++) {
 40:     col = aij->garray[i];
 41:     for (subRank=0; subRank<subCommSize; subRank++) {
 42:       rank = commRankMap[subRank];
 43:       if ((col >= mat->cmap->range[rank]) && (col < mat->cmap->range[rank+1])) {
 44:         garrayCMap[i] = (*subMat)->cmap->range[subRank] + col - mat->cmap->range[rank]+1;
 45:         break;
 46:       }
 47:     }
 48:   }

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

 60:   /* reuse diag block with the new submat */
 61:   MatDestroy(&((Mat_MPIAIJ*)((*subMat)->data))->A);
 62:   ((Mat_MPIAIJ*)((*subMat)->data))->A = aij->A;
 63:   PetscObjectReference((PetscObject)aij->A);

 65:   /* Now traverse aij->B and insert values into subMat */
 66:   for (i=0; i<aij->B->rmap->n; i++) {
 67:     newRow = (*subMat)->rmap->range[subCommRank] + i;
 68:     for (j=aijB->i[i]; j<aijB->i[i+1]; j++) {
 69:       newCol = garrayCMap[aijB->j[j]];
 70:       if (newCol) {
 71:         newCol--; /* remove the increment */
 72:         MatSetValues(*subMat,1,&newRow,1,&newCol,(aijB->a+j),INSERT_VALUES);
 73:       }
 74:     }
 75:   }

 77:   /* assemble the submat */
 78:   MatAssemblyBegin(*subMat,MAT_FINAL_ASSEMBLY);
 79:   MatAssemblyEnd(*subMat,MAT_FINAL_ASSEMBLY);
 80: 
 81:   /* deallocate temporary data */
 82:   PetscFree(commRankMap);
 83:   PetscFree(garrayCMap);
 84:   PetscFree(nnz);
 85:   return(0);
 86: }