NAME

       KURV1 - calculate values for KURV2 usage

SYNOPSIS

       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.

DESCRIPTION

       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.

ACCESS

       To use KURV1, load the NCAR Graphics library ngmath.

SEE ALSO

       kurv2, 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.