CURVP1 - calculate values for CURVP2 usage.

       To use CURVP1, 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                                     CURVP1(3NCARG)

       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 function -- Y(K) is the
                   functional value at X(K) for K=1,N.

       P           (real, input) The period of the function. P must be greater than X(N)-X(1).

       YP          (real, output) Contains values for the second derivative (these are calculated by CURVP1).

       TEMP        (real, input) Scratch space.

       SIGMA       (integer, 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.

       IER         (integer,  output)  An  error  return  value.  If  IER  is returned as 0, then no errors were
                   detected.

                   = 1 if N is less than 2.
                   = 2 if P is less than or equal to X(N)-X(1).
                   = 3 if the X values are not strictly increasing.

       CURVP1 - calculate values for CURVP2 usage.

       curvp2, fitgrid_params.

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

       CALL CURVP1 (N, X, Y, P, YP, TEMP, SIGMA, IER)

       This  subroutine  calculates  certain values that are used by CURVP2 in order to compute an interpolatory
       spline under tension through a sequence  of  functional  values  for  a  periodic  function.  The  actual
       computation of the interpolated values must be done using CURVP2 .