ADAS Subroutine lfitsp

       SUBROUTINE LFITSP(X,XA,N,YAA,Y,DY,I0,C1,C2,C3,C4,ISW)
       IMPLICIT REAL*8(A-H,O-Z)
C-----------------------------------------------------------------------
C                                                                       
C  ************  FORTRAN 77 SUBROUTINE: LFITSP *************************
C                                                                       
C  PURPOSE: SUBROUTINE TO PERFORM SPLINE INTERPOLATION
C
C  LARGER ARRAY DIMENSION VERSION OF NFITSP
C
C  INPUT
C      X       = REQUIRED X-VALUE
C      XA(I)   = X-VALUES
C      N       = NUMBER OF VALUES
C      YAA(I)  = Y-VALUES (POSSIBLY STORED AS MULTIPLE SETS)
C      I0      = STARTING INDEX(-1) IN YAA ARRAY OF REQUIRED INPUT SET
C      C1(I,J) = 1ST SPLINE COEFFICIENT PRECURSOR
C      C2(I,J) = 2ND SPLINE COEFFICIENT PRECURSOR
C      C3(I,J) = 3RD SPLINE COEFFICIENT PRECURSOR
C      C4(I,J) = 4TH SPLINE COEFFICIENT PRECURSOR
C      ISW     = .LE.0  ORDINARY     SPLINE INTERPOLATION
C              = .GT.0  LOGARITHMIC  SPLINE INTERPOLATION
C  OUTPUT
C      Y       = RETURNED Y-VALUE
C      DY      = RETURNED DERIVATIVE
C
C AUTHOR:
C
C  ******** H.P.SUMMERS, JET        7 FEB 1989      **************
C
C UNIX-IDL CONVERSION:
C
C VERSION: 1.1                          DATE: 07-10-96
C MODIFIED: WILLIAM OSBORN
C               - FIRST CONVERTED.
C
C VERSION: 1.2                          DATE: 15-05-07
C MODIFIED: Allan Whiteford
C               - Updated comments as part of subroutine
C                 documentation production.
C
C----------------------------------------------------------------------
      INTEGER             I0,          ISW,         N
      REAL*8              C1(40,39),   C2(40,39),   C3(40,39)
      REAL*8              C4(40,39),   DY,          X,           XA(40)
      REAL*8              Y,           YAA(40)