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From: Arun Kannath on 2 Jun 2010 09:55
Hi, I am trying to perform a non-linear curve fit using the CF tool box. Since my equation is non-linear and different from the default types, I need to choose "Custom Equation" as the Type of fit and press "New equation" button in the "Fitting" tab, seen on the Curve Fitting Tool window. I then use the "General Equations" tab to enter my non-linear eqaution. My equation is of the form y = c*int(f(x),-pi,pi) where f(x) is the funtion I want to integrate between limits -pi and pi. However, the curve fit tool does not seem to recognise "int" and does not consider it as a valid matlab expression.
How can I get around this problem? I cant compute the integral analytically either. Interestingly, the toolbox seems to accept "diff" for differentiation.

Please help.
Thanks
From: Steven Lord on 2 Jun 2010 10:37

"Arun Kannath" <a.kannath(a)geotech.co.uk> wrote in message
news:hu5nrq$c5e$1(a)fred.mathworks.com...
> Hi, I am trying to perform a non-linear curve fit using the CF tool box.
> Since my equation is non-linear and different from the default types, I
> need to choose "Custom Equation" as the Type of fit and press "New
> equation" button in the "Fitting" tab, seen on the Curve Fitting Tool
> window. I then use the "General Equations" tab to enter my non-linear
> eqaution. My equation is of the form y = c*int(f(x),-pi,pi) where f(x)
> is the funtion I want to integrate between limits -pi and pi. However, the
> curve fit tool does not seem to recognise "int" and does not consider it
> as a valid matlab expression.
> How can I get around this problem? I cant compute the integral
> analytically either. Interestingly, the toolbox seems to accept "diff" for
> differentiation.

DIFF is defined for regular old numeric data.

http://www.mathworks.com/access/helpdesk/help/techdoc/ref/diff.html

INT is a method of symbolic objects from Symbolic Math Toolbox ONLY.

http://www.mathworks.com/access/helpdesk/help/toolbox/symbolic/int.html

[Well, okay, technically that's not true ... but the version of INT for char
arrays simply turns the char array into a symbolic object and then calls the
symbolic method.]

I don't believe the CFTOOL or the other Curve Fitting Toolbox methods work
on symbolic objects.

--
Steve Lord
slord(a)mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ
To contact Technical Support use the Contact Us link on
http://www.mathworks.com


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