Re: Fitting a Complicated Function

*To*: mathgroup at smc.vnet.net*Subject*: [mg131477] Re: Fitting a Complicated Function*From*: rdlady at gmail.com*Date*: Fri, 2 Aug 2013 02:50:45 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net*References*: <20120710044030.B3C9A682B@smc.vnet.net> <jtogrl$qll$1@smc.vnet.net>

I'm having a similar problem in Mathematica. When I try to fit data to my formula I get errors like this: p = Fit[data, {1, x, y, k, z, a, b, k/x, z/x, z/y, z/k, a/y, b/x, b/y, b/k, b/z, b/a }, {x, y, k, z, a, b}] MathematicaScript -script script.m | head 1 Power::infy: Infinite expression -- encountered. 0. 1 Power::infy: Infinite expression -- encountered. 0. This is because some "a" and some "b" in my training set are zeros. How can I run linear regression with this formula (x, y, k, z, a, b, k/x, z/x, z/y, z/k, a/y, b/x, b/y, b/k, b/z, b/a ) without changing my a and b values? On Friday, July 13, 2012 2:56:53 AM UTC-4, Peter Klamser wrote: > ... 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 > > >