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FITCS

       REAL FUNCTION  FITCS (T, N, X, A, B, C, D, IT)
 C$    (Evaluate a Cubic Spline at a Point)
 C$    This function interpolates a curve at a given point using a
 C$    cubic spline.  SUBROUTINE FITSM should be called earlier to
 C$    determine certain necessary parameters.
 C$
 C$    On input--
 C$
 C$    T...........ordinate value for which the cubic spline
 C$                interpolant is to be evaluated.
 C$    N...........number of points in X(*).
 C$    X(*)........original ordinate values used to determine
 C$                the spline.
 C$    A(*),B(*),C(*),D(*).....spline polynomial coefficients.
 C$    IT.......... .EQ. 1 - first call.
 C$                 .NE. 1 - subsequent call  (with N, X, A, B, C,
 C$                          D unchanged),  and  this value  of  T
 C$                          larger than the  previous value.   In
 C$                          such  a  case,  the  search  for  the
 C$                          interval  in  which  T  lies  can  be
 C$                          greatly   speeded.    Thus   IT   can
 C$                          frequently be  a  loop index  in  the
 C$                          calling program  if the  values of  T
 C$                          are incremented successively.
 C$
 C$    The parameters  N,  X, A,  B,  C,  and D  should  be  input
 C$    unaltered from the output of SUBROUTINE FITSM.
 C$
 C$    On output--
 C$
 C$    FITCS contains the interpolated value. For T less than
 C$    X(1), FITCS = Y(1).  For T greater than X(N), FITCS = Y(N).
 C$    None of the input parameters are altered.  Adapted from FUNCTION
 C$    FITC2 by
 C$
 C$    Author:  A.K. Cline, "Scalar and Planar Valued Curve Fitting
 C$             Using Splines Under Tension", Comm. A.C.M. 17,
 C$             218-225 (1974).  (Algorithm 476).
 C$
 C$    Modifications by Nelson H.F. Beebe, Department of Chemistry
 C$    Aarhus University,  Aarhus,  Denmark,  to  provide  a  more
 C$    transportable program.
 C$    (03-APR-82)