# ncl_csa2ls - Man Page

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

## Synopsis

CALL CSA2LS (NI, XI, UI, KNOTS, NO, 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.

NO

(integer, input) The number of coordinate values in the output list.  NO can be any positive number.

XO

(real, input) An array dimensioned for NO containing the X coordinates  of the output list.

YO

(real, input) An array dimensioned for NO containing the Y coordinates  of the output list.

UO

(real, output) An array dimensioned for NO containing the calculated  function values for the output spline.  UO(I) is the calculated functional  value at (XO(I),YO(I)) for I=1,NO.

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

CSA2LS is called to find an approximating cubic spline surface for two-dimensional input data with output values calculated at a list of user-specified points.  If you want to weight the input data values, calculate derivatives, or handle data sparse areas specially, then you will need to use CSA2LXS.

## Access

To use CSA2LS, load the NCAR Graphics library ngmath.