ncl_c_ftkurvpd man page

c_ftkurvpd — interpolation and derivative calculation for closed parametric curves

Function Prototype

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

Synopsis

int c_ftkurvpd (n, xi, yi, m, t, xo, yo, xd, yd, xdd, ydd);

Description

n

The number of input data points. (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).

m

The number of desired interpolated points.

t

Contains an array of values for the parameter mapping onto the interpolated curve. Any interval [tt,tt+1.] maps onto the entire curve.

xo

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

yo

An array containing the Y values for the interpolated points.

xd

Contains the first derivatives of the X component with respect to t.

yd

Contains the first derivatives of the Y component with respect to t.

xdd

Contains the second derivatives of the X component with respect to t.

ydd

Contains the second derivatives of the Y component with respect to t.

Return Value

c_ftkurvpd returns an error value as per:

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

Usage

This procedure behaves like ftkurvp except that in addition it returns  the first and second derivatives of the component functions in the parameterization.

Given a sequence of distinct 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[0],y[0]) as well (completing the closed curve).

c_ftkurvpd is called after all of the desired values for control parameters  have been set using the procedures c_ftseti, c_ftsetr, c_ftsetc. The  only control parameter that applies to c_ftkurvpd is: sig.

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).

Access

To use c_ftkurvpd, 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

Info

March 1998 UNIX NCAR GRAPHICS