# csa1s

`csa1s` calculates 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
csa1xs.

**Note:** This function is only available in version 4.1.1 of
NCL. If your site is licensed for version 4.1, then you can get
version 4.1.1 for free. To get version 4.1.1 of NCAR Graphics
software, please contact your site representative. If you don't know
who your site representative is, then send email to ncarginf@ucar.edu or call (303)
497-1201.

## Synopsis

function csa1s(
xi[*] : float,
yi[*] : float,
knots[1] : integer
xo[*] : float
)

## Arguments

*xi*
- A one-dimensional array of any size containing the X coordinates of the
input data points.
*yi*
- A one-dimensional array of the same size as
*xi* containing the Y
coordinates of the input data points.
*
knots
*
- 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.
*xo*
- A one-dimensional array containing the X coordinates of the
output curve.

## Return value

`csa1s` returns an array containing the calculated functional
values. The returned value has the same size as *xo* and
contains functional values for each element of *xo*.

## Description

`csa1s` is in the
csagrid package
- a software package that
implements a cubic spline approximation algorithm to
fit a function to input data. The input for the approximation is
a set of randomly-spaced data. These data may be one-dimensional,
two-dimensional, or three-dimensional.

The general documentation for csagrid contains several
complete examples
for entries in the csagrid package.

## Example

begin
;----------- Define original data --------------------------------------
xi = (/0.0, 0.1, 0.2, 0.3, 0.5, 0.6, 0.65, 0.8, 0.9, 1./)
yi = (/0.0, 0.8, -0.9, -0.9, 0.9, 1.0, 0.90, -0.8, -0.8, 0./)
npts = 101
xo = fspan(0.0,1.0,npts) ; Create the output X coordinate array.
;--- Calculate approximated function values using differing number of knots.
knots = 4
yo = csa1s(xi,yi,knots,xo)
end

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* $Revision: 1.4 $ $Date: 1999/03/19 15:32:23 $ *