CURVI - integrate a spline curve

       To use CURVI, load the NCAR Graphics library ngmath.

       Copyright (C) 2000
       University Corporation for Atmospheric Research

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

UNIX                                               March 1998                                      CURVI(3NCARG)

       XL          (real, input) The lower limit of the integration.

       XR          (real, input) The upper limit of the integration.

       N           (real, 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 function -- Y(K) is the
                   (real, input) 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.

       CURVI - integrate a spline curve

       CURVI returns the integral of the interpolated curve between the specified limits.

       curv1, fitgrid_params.

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

       FUNCTION CURVI (XL, XU, N, X, Y, YP, SIGMA)

       This function calculates an integral between two specified limits.  CURV1 must be called prior to calling
       CURVI, and the values thus obtained used as input to CURVI.  The value of the integral is returned.