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Re: Fitting a Complicated Function


... Mathematica loves complex results, even when there is no need for it.

where are the data?

Peter

2012/7/10  <mpdgeorgin at gmail.com>:
> I'm trying to fit a very complicated function and I'm having some problems.
>
> Right now I'm trying to do a Constrained fit where my parameters are R,m,a.
>
> FindFit[data, {
>   Exp[-x/R] +
>    Exp[-x/R]*
>     Sum[((-a*x^(1 - m))^n)*
>       Hypergeometric1F1[-m*n, 1 + n - m*n, x/R]/
>        Gamma[1 + n - m*n], {n, 1, 15}], 1 < R < 30,
>   0 < a < .5, .4 < m < 1}, {R, m, a}, x]
>
> The error that appears is :
>
> Power:infy : infinite expression
> FindFit:nrmnum : the function value Indeterminate is not a real number at{R,m,a} = {2, 0.94, 0.45}
>
> This is strange because I can evaluate the function at these values and it gives me a real, finite result.
>
> I have a couple questions:
>
> 1) Is there a way to check what the Find fit function is actually doing? As in can I look at the code to see exactly where its going wrong.
>
> 2) What should my next step be? according to my PI, simplification of the function doesn't lead anywhere.
>
> Thanks
>
> Marcel
>



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