ADAS Subroutine ngspc

       SUBROUTINE NGSPC(XA,N,C1,C2,C3,C4)
       IMPLICIT REAL*8(A-H,O-Z)
C-----------------------------------------------------------------------
C  PURPOSE: GENERATE PRECURSORS OF SPLINE COEFFICIENTS SUITABLE
C  FOR BOTH FORWARD AND BACKWARD INTERPOLATION
C
C  INPUT
C      XA(I)=SET OF KNOTS
C      N=NUMBER OF KNOTS  (N.LE.20)
C  OUTPUT
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
C
C
C-----------------------------------------------------------------------
C IDL-UNIX CONVERSION:
C
C  VERSION: 1.1                                        DATE: 01/10/96
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             N
      REAL*8              C1(10,9),    C2(10,9),    C3(10,9)
      REAL*8              C4(10,9),    XA(10)