NAME

       CURVD - derivatives for 1D functions.

SYNOPSIS

       FUNCTION CURVD (T, N, X, Y, YP, SIGMA)

       This  function  calculates a derivative at a specified point using a spline under tension.
       CURV1 must be called prior to calling CURVD, and the values thus obtained used as input to
       CURVD. The derivative value is returned.

DESCRIPTION

       T           (real,  input)  The  abscissa  for  which  an  interpolated  function value is
                   desired.

       N           (integer, input) The number of input data values. (N > 1)

       X           (real, input) An array containing the abscissae for the input function.

       Y           (real, input) An array containing the functional values of the input  data  --
                   Y(K) is the functional value at X(K) for K=1,N.

       YP          (real,  input)  Contains  values  for  the second derivative (as calculated by
                   CURV1).

       SIGMA       (real, input) Tension factor. Values near zero result in a cubic spline; large
                   values (e.g. 50) result in nearly a polygonal line. A typical value is 1.

RETURN VALUE

       CURVD returns the derivative value of the interpolated curve at the specified point T.

ACCESS

       To use CURVD, load the NCAR Graphics library ngmath.

SEE ALSO

       curv1, fitgrid_params.

       Complete documentation for Fitgrid is available at URL
       http://ngwww.ucar.edu/ngdoc/ng/ngmath/fitgrid/fithome.html

COPYRIGHT

       Copyright (C) 2000
       University Corporation for Atmospheric Research

       The use of this Software is governed by a License Agreement.