# ncl_c_csa2lxs - Man Page

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

## Function Prototype

float *c_csa2lxs(int, float [], float [], float [], float [], int [], float, int [], int, float [], float [], int *);

## Synopsis

int c_csa2lxs(int n, float xi[], float yi[], float zi[], float wts[], int knots[2], float smth, int nderiv[2], int no, float xo[], float yo[], int *ier);

## Description

- n
(integer, input) The number of input data points. It must be that n is greater than 3 and, depending on the size of knots below, n may have to be larger.

- xi
(real, input) An array dimensioned for n containing the X coordinate values for the input function.

- yi
(real, input) An array dimensioned for n containing the Y coordinate values for the input function.

- zi
(real, input) An array containing the functional values of the input function -- zi[k] is the functional value at (xi[k], yi[k]) for k=0,n-1.

- wts
(real, input) An array containing weights for the zi values at the input xi and yi values, that is, wts[l] is a weight for the value of zi[l] for l=0,n-1. If you do not desire to weight the input zi values, then set wts[0] to -1. The weights in the wts array are relative and may be set to any non-negative value. When c_csa2lxs is called, the weights are summed and the individual weights are normalized so that the weight sum is unity.

- knots
(integer, input) The number of knots to be used in constructing the approximation spline. knots[0] and knots[1] must be at least 4. The larger the value for knots, the closer the approximated curve will come to passing through the input function values.

- smth
(real, input) A parameter that controls extrapolation into data sparse regions. If smth is zero, then nothing special is done in data sparse regions. A good first choice for smth is 1.

- nderiv
(integer, input) For each of the two coordinate direction, specifies whether you want functional values (nderiv=0), first derivative values (nderiv=1), or second derivative values (nderiv=2). For example, if nderiv[0]=1 and nderiv[1]=1, then the second order mixed partial would be computed.

- no
(integer, input) The number of X - Y coordinate values to be calculated for the output array.

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

- yo
(real, output) An array dimensioned for no containing the Y coordinates of the output list.

- ier
(pointer to 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 error list in the error table for details.

## Usage

c_csa2lxs is called to find values of an approximating cubic spline at specified two-dimensional coordinates. If you want to weight the input data values, calculate derivatives, or handle data sparse areas specially, then you will need to use c_csa2lxs.

c_csa2lxs returns a pointer to a linear array of data that contains the approximated values calculated at the input list of coordinate values. That is, if out is declared as

float *out;

and we set:

out = c_csa2lxs(n, x, y, z, wts, knots, smth, nderiv, no, xo, yo, &ier);

then out[i] is the approximated function value at coordinate point (xo[i], yo[i]) for 0 <= i < no. The space for out is allocated internal to c_csa2lxs and is no floats in size.

## Access

To use c_csa2lxs, load the NCAR Graphics library ngmath.

## See Also

csagrid, c_csa2s, c_csa2xs, c_csa2ls

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.