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MathGroup Archive 2007

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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/


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