RedHat 9 (Linux i386) - man page for pdl::polynomial (redhat section 3)

```Polynomial(3)						User Contributed Perl Documentation					     Polynomial(3)

NAME
PDL::Fit::Polynomial - routines for fitting with polynomials

DESCRIPTION
This module contains routines for doing simple polynomial fits to data

SYNOPSIS
\$yfit = fitpoly1d \$data;

FUNCTIONS
fitpoly1d

Fit 1D polynomials to data using min chi^2 (least squares)

Usage: (\$yfit, [\$coeffs]) = fitpoly1d [\$xdata], \$data, \$order, [Options...]

Signature: (x(n); y(n); [o]yfit(n); [o]coeffs(order))

Uses a standard matrix inversion method to do a least squares/min chi^2 polynomial fit to data. Order=2 is a linear fit (two parameters).

Returns the fitted data and optionally the coefficients.

One can thread over extra dimensions to do multiple fits (except the order can not be threaded over - i.e. it must be one fixed scalar num-
ber like "4").

The data is normalised internally to avoid overflows (using the mean of the abs value) which are common in large polynomial series but the
returned fit, coeffs are in unnormalised units.

\$yfit = fitpoly1d \$data,2; # Least-squares line fit
(\$yfit, \$coeffs) = fitpoly1d \$x, \$y, 4; # Fit a cubic

\$fitimage = fitpoly1d \$image,2  # Fit a quadratic to each row of an image

\$myfit = fitpoly1d \$line, 2, {Weights => \$w}; # Weighted fit

Options:
Weights    Weights to use in fit, e.g. 1/\$sigma**2 (default=1)

BUGS
May not work too well for data with large dynamic range.