Date: 2015-10-02T22:10:23+00:00

Actual source code: lrc.c
petsc-3.6.2 2015-10-02
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      2: #include <petsc/private/matimpl.h>          /*I "petscmat.h" I*/
      3: #include <../src/mat/impls/dense/seq/dense.h>

      5: typedef struct {
      6:   Mat         A,U,V;
      7:   Vec         work1,work2; /* Sequential (big) vectors that hold partial products */
      8:   PetscMPIInt nwork;       /* length of work vectors */
      9: } Mat_LRC;

     15: PetscErrorCode MatMult_LRC(Mat N,Vec x,Vec y)
     16: {
     17:   Mat_LRC        *Na = (Mat_LRC*)N->data;
     19:   PetscScalar    *w1,*w2;

     22:   MatMult(Na->A,x,y);

     24:   /* multiply the local part of V with the local part of x */
     25:   /* note in this call x is treated as a sequential vector  */
     26:   MatMultTranspose_SeqDense(Na->V,x,Na->work1);

     28:   /* Form the sum of all the local multiplies : this is work2 = V'*x =
     29:      sum_{all processors} work1 */

     31:   VecGetArray(Na->work1,&w1);
     32:   VecGetArray(Na->work2,&w2);
     33:   MPI_Allreduce(w1,w2,Na->nwork,MPIU_SCALAR,MPIU_SUM,PetscObjectComm((PetscObject)N));
     34:   VecRestoreArray(Na->work1,&w1);
     35:   VecRestoreArray(Na->work2,&w2);

     37:   /* multiply-sub y = y  + U*work2 */
     38:   /* note in this call y is treated as a sequential vector  */
     39:   MatMultAdd_SeqDense(Na->U,Na->work2,y,y);
     40:   return(0);
     41: }

     45: PetscErrorCode MatDestroy_LRC(Mat N)
     46: {
     47:   Mat_LRC        *Na = (Mat_LRC*)N->data;

     51:   MatDestroy(&Na->A);
     52:   MatDestroy(&Na->U);
     53:   MatDestroy(&Na->V);
     54:   VecDestroy(&Na->work1);
     55:   VecDestroy(&Na->work2);
     56:   PetscFree(N->data);
     57:   return(0);
     58: }

     63: /*@
     64:       MatCreateLRC - Creates a new matrix object that behaves like A + U*V'

     66:    Collective on Mat

     68:    Input Parameter:
     69: +   A  - the (sparse) matrix
     70: -   U. V - two dense rectangular (tall and skinny) matrices

     72:    Output Parameter:
     73: .   N - the matrix that represents A + U*V'

     75:    Level: intermediate

     77:    Notes: The matrix A + U*V' is not formed! Rather the new matrix
     78:           object performs the matrix-vector product by first multiplying by
     79:           A and then adding the other term
     80: @*/
     81: PetscErrorCode  MatCreateLRC(Mat A,Mat U, Mat V,Mat *N)
     82: {
     84:   PetscInt       m,n;
     85:   Mat_LRC        *Na;

     88:   MatGetLocalSize(A,&m,&n);
     89:   MatCreate(PetscObjectComm((PetscObject)A),N);
     90:   MatSetSizes(*N,n,n,PETSC_DECIDE,PETSC_DECIDE);
     91:   PetscObjectChangeTypeName((PetscObject)*N,MATLRC);

     93:   PetscNewLog(*N,&Na);
     94:   (*N)->data = (void*) Na;
     95:   Na->A      = A;

     97:   MatDenseGetLocalMatrix(U,&Na->U);
     98:   MatDenseGetLocalMatrix(V,&Na->V);
     99:   PetscObjectReference((PetscObject)A);
    100:   PetscObjectReference((PetscObject)Na->U);
    101:   PetscObjectReference((PetscObject)Na->V);

    103:   VecCreateSeq(PETSC_COMM_SELF,U->cmap->N,&Na->work1);
    104:   VecDuplicate(Na->work1,&Na->work2);
    105:   Na->nwork = U->cmap->N;

    107:   (*N)->ops->destroy = MatDestroy_LRC;
    108:   (*N)->ops->mult    = MatMult_LRC;
    109:   (*N)->assembled    = PETSC_TRUE;
    110:   (*N)->cmap->N      = A->cmap->N;
    111:   (*N)->rmap->N      = A->cmap->N;
    112:   (*N)->cmap->n      = A->cmap->n;
    113:   (*N)->rmap->n      = A->cmap->n;
    114:   return(0);
    115: }