ADAS Subroutine nfasym

       SUBROUTINE NFASYM(X,XA,N,YA,Y,DY,C1,C2,C3,C4,FORM,IFORMS)
       IMPLICIT REAL*8(A-H,O-Z)
C-----------------------------------------------------------------------
C  PURPOSE: PROVIDE A SPLINE INTERPOLATE MAKING USE OF SPECIFIED
C  ASYMPTOTIC BEHAVIOUR
C
C  USES LABELLED COMMON /SPL3/
C
C  INPUT
C      X=REQUIRED X-VALUE
C      X(I)=KNOTS
C      N=NUMBER OF KNOTS
C      C1(I,J)=1ST SPINE COEFFICIENT PRECURSOR
C      C2(I,J)=2ND SPINE COEFFICIENT PRECURSOR
C      C3(I,J)=3RD SPINE COEFFICIENT PRECURSOR
C      C4(I,J)=4TH SPINE COEFFICIENT PRECURSOR
C      FORM=EXTERNAL FUNCTION SPECIFYING ASYMPTOTIC FORMS
C      IFORMS=INDEX OF REQUIRED FORM
C  OUTPUT
C      Y=RETURNED Y-VALUE
C      DY=RETURNED DERIVATIVE
C
C
C  ***********                                              ***********
C-----------------------------------------------------------------------
C IDL-UNIX CONVERSION:
C
C  VERSION: 1.1                                        DATE: 01/11/96
C  MODIFIED:  WILLIAM OSBORN
C           - FIRST WRITTEN. NO CHANGES.
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-----------------------------------------------------------------------
C-----------------------------------------------------------------------
      INTEGER             IFORMS,      N
      REAL*8              C1(10,9),    C2(10,9),    C3(10,9)
      REAL*8              C4(10,9),    DY,          X,           XA(10)
      REAL*8              Y,           YA(10)