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Topic: adding constraints to curve fitting / least squares code?
Replies: 1   Last Post: Mar 9, 2013 4:53 PM

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John D'Errico

Posts: 9,046
Registered: 12/7/04
Re: adding constraints to curve fitting / least squares code?
Posted: Mar 9, 2013 4:53 PM
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"Andres " <adelahoz@gmail.com> wrote in message <khf2ka$mtq$1@newscl01ah.mathworks.com>...
> Hello.
>
> I am using the curve fitting tool's generated code to obtain coefficient values for different functions that I'm adjusting to some data.
>
> One problem I often encounter with the data sets, though, is that the best fit that the code finds for the coefficients leads to a negative slope at the very beginning of the data. Since I'm doing this to obtain a material model, this initial negative slope doesn't really make sense and will cause computing problems when I use the coefficient values in a model. So the ideal solution would be to make the code such that the slope is always positive in the range of the minimum and maximum x-values.
>
> I can solve this by constraining the coefficient values either on CFTOOL or in the code itself. But I'd prefer to do it automatically, by a code, since this way I have to keep rewriting things. Is there an 'easy' way of doing this (i.e. adding a code to the current cftool-generated code that forces a condition), or would I have to start from scratch?
>
> This is a sample of the code:
>


(snip)

>
> Any help would be appreciated.


Use a tool (SLM) that is designed from the start to help
you do this.

http://www.mathworks.com/matlabcentral/fileexchange/24443-slm-shape-language-modeling

If you want the slope to be nonnegative at the left end, there is a
simple way to specify that.

HTH,
John



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