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Topic: Curve fit tool (cftool) and custom equations
Replies: 2   Last Post: Feb 21, 2009 12:46 AM

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Bob Pownall

Posts: 261
Registered: 12/7/04
Curve fit tool (cftool) and custom equations
Posted: Feb 20, 2009 2:04 PM
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Summary: I'm having problems correctly entering my custom equation in
the curve fit tool. Is there a better way?

I'm running MATLAB 7.1 (R14) Student Version with the Curve Fitting
Toolbox version 1.1.4.

I'm trying to fit a custom equation to my data. Based on theoretical
concerns, I expect the fit to involve a decaying exponential and a
couple of error functions.

When I try to enter the custom equation in the "Create Custom Equations"
editor, I apparently always screw up something because the resulting fit
is a straight line. However, when I try coding the equation in an
m-file, I can hand-adjust the parameters to get a reasonably good fit.

Is there a better way to enter custom equations? Is there some way I
can take my m-file, or a modified version of it, and tell cftool to use
that as the custom equation? Am I missing something obvious?

Bob Pownall

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