# ncl_csa2s - Man Page

cubic spline approximation, simple entry for two-dimensional input, gridded output

## Synopsis

CALL CSA2S (NI, XI, UI, KNOTS, NXO, ,NYO, XO, YO, 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 coordinates of the input data points. XI is dimensioned for 2 x NI. XI(1,L) is the X coordinate and XI(2,L) is the Y 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 the coordinate (XI(1,L),XI(2,L)) for L=1,NI.

- KNOTS
(integer, input) The number of knots to be used in constructing the approximation spline. KNOTS is dimensioned for 2 and provides the number of knots to be used in the X and the Y directions. Both KNOTS(1) and KNOTS(2) must be at least 4. The larger the values 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.

- 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.

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

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

CSA2S is called to find an approximating cubic spline surface for two-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 CSA2XS.

## Access

To use CSA2S, load the NCAR Graphics library ngmath.

## See Also

csagrid, csa2xs, csa2ls, csa2lxs

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.