Re: Fitting a Complicated Function

*To*: mathgroup at smc.vnet.net*Subject*: [mg127278] Re: Fitting a Complicated Function*From*: Peter Klamser <klamser at googlemail.com>*Date*: Fri, 13 Jul 2012 02:55:02 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*References*: <20120710044030.B3C9A682B@smc.vnet.net>

... 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 >

**References**:**Fitting a Complicated Function***From:*mpdgeorgin@gmail.com