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Re: Exponential fit question.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg27992] Re: Exponential fit question.
  • From: "Paul Lutus" <nospam at nosite.com>
  • Date: Wed, 28 Mar 2001 02:40:21 -0500 (EST)
  • References: <99pdg6$lft@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"joe" <joe at wam.umd.edu> wrote in message news:99pdg6$lft at smc.vnet.net...
> hello.
>
> I was wondering if someone could help me with the following problem.
>
> I am trying to perform an exponential fit to the following data
> {{x,y}}
>
> data
> ={{50,22},{64,62},{78,122},{93,269},{107,414},{122,507},{136,597}}
>
> Fit[data,Exp[x],x]
>
> what I get is
>
> 1.94272422061017735^-63 *E^x Which is not correct.
>
> With Excel I get 7.5*E^0.0034x which is correct.
>
> How can I do this with Mathematica ?

Excel's exponential regression method is not particularly useful, because it
relies on a fractional power. This creates all kinds of problems in
mathematical manipulations. Also, the result you posted doesn't fit the data
very well at all -- have you tried to graph it in Excel to see how poorly it
fits the data?

If you do this, you will notice even a linear regression (y = m x + b) does
a better job of fitting the data.

Why not perform another kind of fit? Virtually any other fit is better
suited to the data.

--
Paul Lutus
www.arachnoid.com





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