------------------------------------------------------------------------
IMSL Name:  LFIDS/DLFIDS (Single/Double precision version)
 
Revised:    May 31, 1991
 
Purpose:    Use iterative refinement to improve the solution of a
            real symmetric positive definite system of linear
            equations.
 
Usage:      CALL LFIDS (N, A, LDA, FAC, LDFAC, B, X, RES)
 
Arguments:
   N      - Number of equations.  (Input)
   A      - N by N matrix containing the symmetric positive
            definite coefficient matrix of the linear system.
            (Input)
            Only the upper triangle of A is referenced.
   LDA    - Leading dimension of A exactly as specified in the
            dimension statement of the calling program.  (Input)
   FAC    - N by N matrix containing the trans(R)*R factorization
            of the coefficient matrix A as output from routine
            LFCDS/DLFCDS or LFTDS/DLFTDS.  (Input)
            trans(R) represents the transpose of R.  Only the upper
            triangle of FAC is used.
   LDFAC  - Leading dimension of FAC exactly as specified in the
            dimension statement of the calling program.  (Input)
   B      - Vector of length N containing the right-hand side of
            the linear system.  (Input)
   X      - Vector of length N containing the solution to the
            linear system.  (Output)
   RES    - Vector of length N containing the residual vector at
            the improved solution.  (Output)
 
Remark:
   Informational error
   Type Code
     3   2  The input matrix is too ill-conditioned for iterative
            refinement to be effective.
 
GAMS:       D2b1b
 
Chapter:    MATH/LIBRARY Linear Systems
 
Page No.:   MATH/LIBRARY User's Manual page 83