# ncl_kurv1 - Man Page

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.