1: #define PETSCMAT_DLL

 3:  #include include/private/matimpl.h

  7: /*@
  8:    MatGetColumnVector - Gets the values from a given column of a matrix.

 10:    Not Collective

 12:    Input Parameters:
 13: +  A - the matrix
 14: .  yy - the vector
 15: -  c - the column requested (in global numbering)

 17:    Level: advanced

 19:    Notes:
 20:    Each processor for which this is called gets the values for its rows.

 22:    Since PETSc matrices are usually stored in compressed row format, this routine
 23:    will generally be slow.

 25:    The vector must have the same parallel row layout as the matrix.

 27:    Contributed by: Denis Vanderstraeten

 29: .keywords: matrix, column, get 

 31: .seealso: MatGetRow(), MatGetDiagonal()

 33: @*/
 34: PetscErrorCode  MatGetColumnVector(Mat A,Vec yy,PetscInt col)
 35: {
 36:   PetscScalar        *y,zero = 0.0;
 37:   const PetscScalar  *v;
 38:   PetscErrorCode     ierr;
 39:   PetscInt           i,j,nz,N,Rs,Re,rs,re;
 40:   const PetscInt     *idx;
 41:   MPI_Comm           comm;
 42: 

 47:   if (col < 0)  SETERRQ1(PETSC_ERR_ARG_OUTOFRANGE,"Requested negative column: %D",col);
 48:   MatGetSize(A,PETSC_NULL,&N);
 49:   if (col >= N)  SETERRQ2(PETSC_ERR_ARG_OUTOFRANGE,"Requested column %D larger than number columns in matrix %D",col,N);

 51:   MatGetOwnershipRange(A,&Rs,&Re);

 53:   PetscObjectGetComm((PetscObject)yy,&comm);
 54:   VecGetOwnershipRange(yy,&rs,&re);
 55:   if (Rs != rs || Re != re) SETERRQ4(PETSC_ERR_ARG_INCOMP,"Matrix %D %D does not have same ownership range (size) as vector %D %D",Rs,Re,rs,re);

 57:   VecSet(yy,zero);
 58:   VecGetArray(yy,&y);

 60:   for (i=Rs; i<Re; i++) {
 61:     MatGetRow(A,i,&nz,&idx,&v);
 62:     if (nz && idx[0] <= col) {
 63:       /*
 64:           Should use faster search here 
 65:       */
 66:       for (j=0; j<nz; j++) {
 67:         if (idx[j] >= col) {
 68:           if (idx[j] == col) y[i-rs] = v[j];
 69:           break;
 70:         }
 71:       }
 72:     }
 73:     MatRestoreRow(A,i,&nz,&idx,&v);
 74:   }

 76:   VecRestoreArray(yy,&y);
 77:   return(0);
 78: }