KURV1 - calculate values for KURV2 usage

       To use KURV1, 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                                      KURV1(3NCARG)

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

       X           (real, input) An array containing the X values of the points.

       Y           (real,  input) An array containing the Y values of the points.  Adjacent pairs of points must
                   be distinct.

       SLP1        (real, input) A value (in radians) containing the  slope  at  (X(1),Y(1)).   The  angles  are
                   measured  counter-clockwise from the X axis and the positive sense of the curve is assumed to
                   be that moving from point 1 to point N. A value for SLP1 may be omitted as indicated  by  the
                   switch ISLPSW.

       SLPN        (real,  input)  A  value  (in  radians)  containing  the slope at (X(N),Y(N)). The angles are
                   measured counter-clockwise from the X axis and the positive sense of the curve is assumed  to
                   be  that  moving from point 1 to point N. A value for SLP2 may be omitted as indicated by the
                   switch ISLPSW.

       ISLPSW      (integer, input) A switch to indicate  whether  the  slopes  at  the  end  points  should  be
                   calculated internally.

                   = 0 if SLP1 and SLPN are user-specified.
                   = 1 if SLP1 is user-specified, but SLPN calculated internally.
                   = 2 if SLPN is user-specified, but SLP1 calculated internally.
                   = 3 if SLP1 and SLPN are internally calculated.

       XP          (real, output) An array of length N.

       YP          (real, output) An array of length N.

       TEMP        (real, input) Scratch space.

       S           (real,  input)  An  array  of length N. On output, S contains the polygonal arclengths of the
                   curve.

       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.

       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 a pair of adjacent points coincide.

       KURV1 - calculate values for KURV2 usage

       kurv2, fitgrid_params.

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

       CALL KURV1  (N, X, Y, SLP1, SLPN, ISLPSW, XP, YP, TEMP, S, SIGMA, IER)

       This  subroutine  calculates  certain  values that are used by KURV2 in order to compute an interpolatory
       spline under tension through  a  sequence  of  points  in  the  plane.  The  actual  computation  of  the
       interpolated values must be done using KURV2.