dapply_ilu_udia_l 

Apply ILU preconditioner for unsymmetric diagonal storage

FORMAT

  DAPPLY_ILU_UDIA_L (job, plu, iplu, ndim, nz, x, y, n)

Arguments

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

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

                      job = 1 : y = inverse(transp(L)) * 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 two-dimensional array with dimensions ndim
                      by nz, containing information for use by the ILU
                      preconditioner.
                      On exit, plu is unchanged.

  iplu                integer*4
                      On entry, a one-dimensional array of length at least
                      nz, containing the distances of the diagonals of PLU
                      from the main diagonal.
                      On exit, iplu is unchanged.

  ndim                integer*4
                      On entry, the leading dimension of array A, as declared
                      in the calling subprogram; ndim >= n.
                      On exit, ndim is unchanged.

  nz                  integer*4
                      On entry, the number of diagonals 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_UDIA_L applies the Incomplete LU preconditioner (lower
  triangular part) for a sparse matrix stored using the unsymmetric diagonal
  storage scheme. The input arrays, PLU and IPLU, contain information for use
  by the routine. These arrays are generated by a call to the routine
  DCREATE_ILU_UDIA prior to a call to one of the solvers with Incomplete LU
  preconditioning.  Depending on the value of the input parameter job,
  DAPPLY_ILU_UDIA_L  operates on either the matrix or its transpose.