dapply_ilu_genr_u 

Apply incomplete LU preconditioner for general storage by rows

FORMAT

  DAPPLY_ILU_GENR_U (job, plu, iplu, jplu, nz, x, y, n)

Arguments

  job                 integer*4
                      On entry, defines the operation to be performed:

                      job = 0 : y = inverse(U) * x

                      job = 1 : y = inverse(transp(U)) * x
                      where the incomplete factorization is calculated as L *
                      U.  L and U are lower and upper triangular matrices,
                      respectively.
                      On exit, job is unchanged.

  plu                 real*8
                      On entry, a one-dimensional array of length at least nz
                      containing information used by the Incomplete LU
                      preconditioner.
                      On exit, plu is unchanged.

  iplu                integer*4
                      On entry, a one-dimensional array of length at least
                      n+1, containing the starting indices of each row in
                      array PLU and JPLU.  IPLU is identical to the array IA
                      used in the storage of the matrix A.
                      On exit, iplu is unchanged.

  jplu                integer*4
                      On entry, a one dimensional array of length at least
                      nz, containing the column values of each nonzero
                      element of the matrix PLU, stored using the general
                      storage by rows scheme.  JPLU is identical to the array
                      JA used in the storage of the matrix A in the general
                      storage by rows scheme.
                      On exit, jplu is unchanged.

  nz                  integer*4
                      On entry, the number of nonzero elements stored in
                      array PLU.
                      On exit, nz is unchanged.

  x                   real*8
                      On entry, a one-dimensional array of length at least n,
                      containing the elements of vector x, accessed with unit
                      increment.
                      On exit, x is unchanged.

  y                   real*8
                      On entry, a one-dimensional array of length at least n.
                      On exit, array Y is overwritten by the output vector y.
                      The elements of array Y are accessed with unit
                      increment.

  n                   integer*4
                      On entry, the order of the matrix A.
                      On exit, n is unchanged.

Description

  DAPPLY_ILU_GENR_U applies the Incomplete LU preconditioner (upper
  triangular part) for a sparse matrix stored using the general storage by
  rows scheme. The input arrays, PLU, IPLU and JPLU, contain information for
  use by the routine. These arrays are generated by a call to the routine
  DCREATE_ILU_GENR prior to a call to one of the iterative solvers with
  Incomplete LU preconditioning. The information in the arrays IPLU and JPLU
  is identical to the information in the arrays IA and JA. Therefore, the
  routine DCREATE_ILU_GENR does not generate these arrays.

  Depending on the value of the input parameter job, DAPPLY_ILU_GENR_U
  operates  on either the matrix or its transpose.