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Topic: Curve fitting tool using custom equations
Replies: 1   Last Post: Mar 12, 2013 9:48 AM

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Torsten

Posts: 1,477
Registered: 11/8/10
Re: Curve fitting tool using custom equations
Posted: Mar 12, 2013 9:48 AM
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"Dante Ian Detera" wrote in message <khna0b$js5$1@newscl01ah.mathworks.com>...
> I am trying to curve fit a set of data (in x-y plot/form) into an equation using curve fitting tool in mat lab.
>
> The custom equation is:
> y=a*(1-erf(x/(2*sqrt(b*(7.88e+08)))))
>
> Starting point of a is 1
> Starting point of b is 1e-08
>
> I awlays get an error saying:
> Fit could not be computed due to error:
>
> Error in fittype expression ==> a.*(1-erf(x./(2.*sqrt(b.*(7.88e+08)))))
> ??? Input must be real.
>
> I have no idea how to debug this one. Help please.
>
> Thanks,
> Dante


Does the error disappear if you choose the custom equation as
y=a*(1-erf(x/(2*sqrt(b^2*(7.88e+08)))))
?

Best wishes
Torsten.



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