# ncl_c_csa1s - Man Page

cubic spline approximation, simple entry for one-dimensional input

## Function Prototype

`float *c_csa1s(int, float [], float [], int, int, float [], int *);`

## Synopsis

```float *c_csa1s(int n, float xi[], float yi[], int knots,
int m, float xo[], 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 abscissae  for the input function.

yi

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

knots

(integer, input) The number of knots to be used in constructing the  approximation spline.  knots 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.

m

(integer, input) The number of values to be calculated for the output curve.

xo

(real, input) An array dimensioned for m containing the X coordinates of the output curve.

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_csa1s is called to find an approximating cubic spline for  one-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 c_csa1xs.

c_csa1s returns a pointer to  a linear array of data that is the approximated curve.

## Access

To use c_csa1s, load the NCAR Graphics library ngmath.

## See Also

csagrid, c_csa1xs, c_csa1ls, c_csa1lxs

Complete documentation for Csagrid is available at URL
http://ngwww.ucar.edu/ngdoc/ng/ngmath/csagrid/csahome.html

## Info

January 1999 UNIX NCAR GRAPHICS