# ncl_curvd man page

CURVD — derivatives for 1D functions.

## Synopsis

`FUNCTION CURVD (T, N, X, Y, YP, SIGMA) `

This function calculates a derivative at a specified point using a spline under tension. CURV1 must be called prior to calling CURVD, and the values thus obtained used as input to CURVD. The derivative value is returned.

## Description

- T
- (real, input) The abscissa for which an interpolated function value is desired.
- 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 data -- Y(K) is the functional value at X(K) for K=1,N.
- YP
- (real, input) Contains values for the second derivative (as calculated by CURV1).
- 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.

## Return Value

CURVD returns the derivative value of the interpolated curve at the specified point T.

## Access

To use CURVD, load the NCAR Graphics library ngmath.

## See Also

curv1, fitgrid_params.

Complete documentation for Fitgrid is available at URL

http://ngwww.ucar.edu/ngdoc/ng/ngmath/f…

## Copyright

Copyright (C) 2000

University Corporation for Atmospheric Research

The use of this Software is governed by a License Agreement.

## Info

March 1998 UNIX NCAR GRAPHICS