Re: rather complicated NonlinearFit

*To*: mathgroup at smc.vnet.net*Subject*: [mg73063] Re: [mg73061] rather complicated NonlinearFit*From*: "Chris Chiasson" <chris at chiasson.name>*Date*: Thu, 1 Feb 2007 02:42:46 -0500 (EST)*References*: <200701310556.AAA18035@smc.vnet.net>

You might be able to construct a better fit by manually setting up the optimization and then choosing initial values that are your guesses for the parameters of the model. Finally, *if* your model is correct, I think the residuals will be normally distributed about the prediction of the function. In other words: (correctFunction/@xdata)-functionData should give a list of normally distributed numbers On 1/30/07, fonfastik at interia.pl <fonfastik at interia.pl> wrote: > Hello, > I would like to model a chemical decomposition reaction with > adsorption of one of the reagents. > I determined an equation I would like to fit to my data (conversion of > the reagent vs temperature), > > here is the formula of the equation: > 1-Exp[-0.5 (A1 Exp[-E1/(8.31 x)] (1-(Sqrt[((A1 Exp[-E1/(8.31 x)])/(A2 > Exp[-E2/(8.31 x)]+A3 Exp[-E3/(8.31 x)])) 0.05])/(1+Sqrt[((A1 Exp[-E1/ > (8.31 x)])/(A2 Exp[-E2/(8.31 x)]+A3 Exp[-E3/(8.31 x)])) 0.05]))+A3 > Exp[-E3/(8.31 x)] ((Sqrt[((A1 Exp[-E1/(8.31 x)])/(A2 Exp[-E2/(8.31 x)] > +A3 Exp[-E3/(8.31 x)])) 0.05])/(1+Sqrt[((A1 Exp[-E1/(8.31 x)])/(A2 > Exp[-E2/(8.31 x)]+A3 Exp[-E3/(8.31 x)])) 0.05])))], > {x},{A1, A2, A3,E1, E2, E3} > > here it is shown more clearly: > http://www.chemia.uj.edu.pl/%7Estelmach/equationfull.GIF > > I am quite confident that the expression is OK, however Mathematica > returns errors about overflow > > may it be that the equation is too complicated? or rather it can't > return good results due to wrong construction? > > should anyone want to give it a try, here you can find a csv file with > data: > http://www.chemia.uj.edu.pl/~stelmach/fitfile.csv > > Regards to all > > -- http://chris.chiasson.name/

**Follow-Ups**:**Re: Re: rather complicated NonlinearFit***From:*Darren Glosemeyer <darreng@wolfram.com>