# ncl_csa3s - Man Page

cubic spline approximation, simple entry for three-dimensional input

## Synopsis

CALL CSA3S (NI, XI, UI, KNOTS, NXO, NYO, NZO, XO, YO, ZO,

UO, NWRK, WORK, IER)

## Description

- NI
(integer,input) The number of input data points. It must be that NI .gt. 3 and, depending on the size of KNOTS below, NI may have to be larger.

- XI
(real, input) An array containing the X - Y - Z coordinates of the input data points. XI is dimensioned for 3 x NI. XI(1,L) is the X coordinate, XI(2,L) is the Y coordinate, and XI(2,L) is the Z coordinate for the input domain for L=1,NI.

- UI
(real, input) An array dimensioned for NI containing function values at the input XI values, that is, UI(L) is the value of the input function at XI(L) for L=1,NI.

- KNOTS
(integer, input) An array dimensioned for 3 containing the number of knots to be used in each coordinate direction for constructing the approximation spline. KNOTS(I) must be at least 4 for I=1,3. The larger the value for KNOTS, the closer the approximated curve will come to passing through the input function values.

- NXO
(integer, input) The number of X coordinate values in the output grid.

- NYO
(integer, input) The number of Y coordinate values in the output grid.

- NZO
(integer, input) The number of Z coordinate values in the output grid.

- XO
(real, input) An array dimensioned for NXO containing the X coordinates of the output surface.

- YO
(real, input) An array dimensioned for NYO containing the Y coordinates of the output surface.

- ZO
(real, input) An array dimensioned for NZO containing the Y coordinates of the output surface.

- UO
(real, output) An array dimensioned for NXO x NYO x NZO containing the calculated function values for the output function. UO(I,J,K) is the calculated functional value at (XO(I), YO(J), ZO(K)) for I=1,NXO and J=1,NYO and K=1,NZO.

- NWRK
(integer, input) The size of the WORK array. NWRK must be at least NK * (NK+3) where NK = KNOTS(1) * KNOTS(2) * KNOTS(3).

- WORK
(real, input) A work array dimensioned for NWRK.

- IER
(integer, output) An error return value. If IER is returned as 0, then no errors were detected. If IER is non-zero, then refer to the man page for csagrid_errors for details.

## Usage

CSA3S is called to find an approximating cubic spline for three-dimensional input data. If you want to weight the input data values, calculate derivatives, or handle data sparse areas specially, then you will need to use CSA3S.

## Access

To use CSA3XS, load the NCAR Graphics library ngmath.

## See Also

csagrid, csa3xs, csa3ls, csa3lxs

Complete documentation for Csagrid is available at URL

http://ngwww.ucar.edu/ngdoc/ng/ngmath/csagrid/csahome.html

## Copyright

Copyright (C) 2000

University Corporation for Atmospheric Research

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