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      SUBROUTINE slSMAT (N, A, Y, D, JF, IW)

     - - - - -
      S M A T
     - - - - -

  Matrix inversion & solution of simultaneous equations
  (single precision)

  For the set of n simultaneous equations in n unknowns:
     A.Y = X

  where:
     A is a non-singular N x N matrix
     Y is the vector of N unknowns
     X is the known vector

  SMATRX computes:
     the inverse of matrix A
     the determinant of matrix A
     the vector of N unknowns

  Arguments:

     symbol  type dimension           before              after

       N      int                 no. of unknowns       unchanged
       A      real  (N,N)             matrix             inverse
       Y      real   (N)              vector            solution
       D      real                       -             determinant
     * JF     int                        -           singularity flag
       IW     int    (N)                 -              workspace

  *  JF is the singularity flag.  If the matrix is non-singular,
    JF=0 is returned.  If the matrix is singular, JF=-1 & D=0.0 are
    returned.  In the latter case, the contents of array A on return
    are undefined.

  Algorithm:
     Gaussian elimination with partial pivoting.

  Speed:
     Very fast.

  Accuracy:
     Fairly accurate - errors 1 to 4 times those of routines optimized
     for accuracy.

  Note:  replaces the obsolete slSMATRX routine.

  P.T.Wallace   Starlink   10 September 1990

  Copyright (C) 1995 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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