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MathGroup Archive 2007

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rather complicated NonlinearFit

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73061] rather complicated NonlinearFit
  • From: fonfastik at interia.pl
  • Date: Wed, 31 Jan 2007 00:56:52 -0500 (EST)

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


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