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.\"
.IX Title "Polynomial 3pm"
.TH Polynomial 3pm "2023-06-17" "perl v5.36.0" "User Contributed Perl Documentation"
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.SH "NAME"
PDL::Fit::Polynomial \- routines for fitting with polynomials
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module contains routines for doing simple
polynomial fits to data
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    $yfit = fitpoly1d $data;
.Ve
.SH "FUNCTIONS"
.IX Header "FUNCTIONS"
.SS "fitpoly1d"
.IX Subsection "fitpoly1d"
Fit 1D polynomials to data using min chi^2 (least squares)
.PP
.Vb 1
\& Usage: ($yfit, [$coeffs]) = fitpoly1d [$xdata], $data, $order, [Options...]
.Ve
.PP
.Vb 1
\&  Signature: (x(n); y(n); [o]yfit(n); [o]coeffs(order))
.Ve
.PP
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).
.PP
Returns the fitted data and optionally the coefficients.
.PP
One can broadcast over extra dimensions to do multiple fits (except
the order can not be broadcasted over \- i.e. it must be one fixed
scalar number like \*(L"4\*(R").
.PP
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.
.PP
.Vb 2
\&  $yfit = fitpoly1d $data,2; # Least\-squares line fit
\&  ($yfit, $coeffs) = fitpoly1d $x, $y, 4; # Fit a cubic
\&  
\&  $fitimage = fitpoly1d $image,3  # Fit a quadratic to each row of an image
\&  
\&  $myfit = fitpoly1d $line, 2, {Weights => $w}; # Weighted fit
.Ve
.PP
.Vb 2
\&  Options:
\&     Weights    Weights to use in fit, e.g. 1/$sigma**2 (default=1)
.Ve
.SH "BUGS"
.IX Header "BUGS"
May not work too well for data with large dynamic range.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\*(L"polyfit\*(R" in PDL::Slatec
.SH "AUTHOR"
.IX Header "AUTHOR"
This file copyright (C) 1999, Karl Glazebrook (kgb@aaoepp.aao.gov.au).
All rights reserved. There
is no warranty. You are allowed to redistribute this software
documentation under certain conditions. For details, see the file
\&\s-1COPYING\s0 in the \s-1PDL\s0 distribution. If this file is separated from the
\&\s-1PDL\s0 distribution, the copyright notice should be included in the file.