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Curve fitting - polynomial fit help

From: Xierxes
Subject: Curve fitting - polynomial fit help
Date: Fri, 25 May 2007 17:58:01 -0700 (PDT)

Hi all,

I am new to Octave and I am trying to fit some experimental data using a
simple quadratic. I have already fit the data in gnuplot, but I need to
develop more complex fitting curves - hence my move to Octave.  The problem
that I am having is that the coefficients generated by gnuplot do not match
the ones generated by the polyfit, wpolyfit or leasqr (I modified the
leasqrdemo to use a quadratic fit, and suit my data) functions. However when
plotted the gnuplot fit looks much closer to experimental data.  I am new to
curve fitting and as a result I am not sure where to go next.

I thought that gnuplot and leasqr used the same method for calculating the
coefficients, hence I am somewhat lost. Anyway back to my probability and
statistics for the engineer and scientist - Any help anyone could provide
would be fantastic,

I am using the latest Octave (2.9.12 and the Optim package from
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