Actual source code: lrc.c
petsc-3.7.1 2016-05-15
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      2: #include <petsc/private/matimpl.h>          /*I "petscmat.h" I*/

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

     11: PETSC_INTERN PetscErrorCode MatMultTranspose_SeqDense(Mat,Vec,Vec);
     12: PETSC_INTERN PetscErrorCode MatMultAdd_SeqDense(Mat,Vec,Vec,Vec);

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

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

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

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

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

     38:   /* multiply-sub y = y  + U*work2 */
     39:   /* note in this call y is treated as a sequential vector  */
     40:   MatMultAdd_SeqDense(Na->U,Na->work2,y,y);
     41:   return(0);
     42: }

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

     52:   MatDestroy(&Na->A);
     53:   MatDestroy(&Na->U);
     54:   MatDestroy(&Na->V);
     55:   VecDestroy(&Na->work1);
     56:   VecDestroy(&Na->work2);
     57:   PetscFree(N->data);
     58:   return(0);
     59: }

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

     67:    Collective on Mat

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

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

     76:    Level: intermediate

     78:    Notes: The matrix A + U*V' is not formed! Rather the new matrix
     79:           object performs the matrix-vector product by first multiplying by
     80:           A and then adding the other term
     81: @*/
     82: PetscErrorCode  MatCreateLRC(Mat A,Mat U, Mat V,Mat *N)
     83: {
     85:   PetscInt       m,n;
     86:   Mat_LRC        *Na;

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

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

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

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

    108:   (*N)->ops->destroy = MatDestroy_LRC;
    109:   (*N)->ops->mult    = MatMult_LRC;
    110:   (*N)->assembled    = PETSC_TRUE;
    111:   (*N)->cmap->N      = A->cmap->N;
    112:   (*N)->rmap->N      = A->cmap->N;
    113:   (*N)->cmap->n      = A->cmap->n;
    114:   (*N)->rmap->n      = A->cmap->n;
    115:   return(0);
    116: }