NonLinearRegress question

*To*: mathgroup at smc.vnet.net*Subject*: [mg12860] NonLinearRegress question*From*: Easan Siviniah <easan at mrl.ucsb.edu>*Date*: Wed, 17 Jun 1998 00:28:03 -0400*Organization*: University of California, Santa Barbara*Sender*: owner-wri-mathgroup at wolfram.com

Hi folks, I'm writing some data fitting code on Mathematica that uses the add-on package 'NonLinearRegress'. However I'm currently stumped because the model I use for fitting involves the use of conditional 'Ifs'. It seems that Mathematica does not recoginise such a function as numerical. Does Anyone have an idea of how to get round this. I've included a typical but simplified example below. In[1] Clear[fun,t,x,y] fun[t_,x_,y_]:=If[t<10,t^2 x + Log[t] y, t^3 x + Log[t] y] data=Table[{t,N[fun[t,2,3]]},{t,1,21,2}] Out[1] {{1,2.},{3,21.2958},{5,54.8283},{7,103.838},{9,168.592},{11,2669.19},{13, 4401.69},{15,6758.12},{17,9834.5},{19,13726.8},{21,18531.1}} In[2] << Statistics`NonlinearFit` NonlinearRegress[data, N[func[t,a,b]] ,z, {{a,{-100,-101}},{b,{2,3}}}, RegressionReport -> BestFitParameters, Method->FindMinimum, ShowProgress -> True] Out[2] NonlinearRegress::"nonnum": "The model is not numerical at (******) Check that all model parameters are included in the parameter list.