NAME

       c_ftkurv - interpolation for parametric curves

FUNCTION PROTOTYPE

       int c_ftkurv (int, float [], float [], int, float [], float [], float []);

SYNOPSIS

       int c_ftkurv (n, xi, yi, m, t, xo, yo);

DESCRIPTION

       n           The number of input data values. (n > 1)

       xi          An array containing the abscissae for the input function.

       yi          An  array  containing  the  functional values (y[k] is the functional value at
                   x[k] for k=0,n-1).

       m           The number of desired interpolated values.

       t           Contains an array of values for the parameter mapping  onto  the  interpolated
                   curve.

       xo          An  array  containing  the X values for the interpolated points.  t[k] maps to
                   (xo[k],yo[k]) for k=0,m-1.

       yo          An array containing the Y values for the interpolated points.   t[k]  maps  to
                   (xo[k],yo[k]) for k=0,m-1.

RETURN VALUE

       c_ftkurv returns an error value as per:

       = 0 -- no error.
       = 1 -- if n is less than 2.
       = 2 -- if adjacent coordinate pairs coincide.

USAGE

       This  function  calculates  an  interpolatory  spline  under tension through a sequence of
       points in the plane.

       Given a sequence of input points ( (x[0],y[0]), ... ,  (x[n-1],y[n-1]),  the  interpolated
       curve  is  parameterized  by  mapping points in the interval [0.,1.] onto the interpolated
       curve. The resulting curve has a parametric representation both of  whose  components  are
       splines  under  tension  and functions of the polygonal arc length. The value 0. is mapped
       onto (x[0],y[0]) and the value 1. is mapped onto (x[n-1],y[n-1]).

       c_ftkurv is called after all of the desired values for control parameters  have  been  set
       using  the  procedures  c_ftseti,  c_ftsetr,  c_ftsetc.  Control  parameters that apply to
       c_ftkurv are: sig, sl1, sln, sf1.

       The value for the parameter sig specifies the 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. (the default).

       The value for parameter sl1 is in radians and contains the slope at (x[0],y[0]). The angle
       is  measured  counter-clockwise  from  the  X  axis and the positive sense of the curve is
       assumed to be that moving from point 0 to point n-1. A value for sl1  may  be  omitted  as
       indicated by the switch sf1.

       The  value  for parameter sln is in radians and contains the slope at (x[n-1],y[n-1]). The
       angle is measured counter-clockwise from the X axis and the positive sense of the curve is
       assumed  to  be  that  moving from point 0 to point n-1. A value for sln may be omitted as
       indicated by the switch sf1.

       The value of sf1 controls whether to use the values for sl1  and  sln,  or  compute  those
       values internally.  Specifically, sf1

       = 0 if sl1 and sln are user-specified.
       = 1 if sl1 is user-specified, but sln is internally calculated.
       = 2 if sln is user-specified, but sl1 is internally calculated.
       = 3 if sl1 and sln are internally calculated.

ACCESS

       To use c_ftkurv, load the NCAR Graphics library ngmath.

SEE ALSO

       fitgrid_params, c_ftseti, c_ftsetr, c_ftsetc.

       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.