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Re: Exponential fit question.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg28029] Re: [mg27986] Exponential fit question.
  • From: Tomas Garza <tgarza01 at prodigy.net.mx>
  • Date: Wed, 28 Mar 2001 02:41:02 -0500 (EST)
  • References: <200103270626.BAA21789@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

To start with, by looking at a plot of your data I don't think you can fit
an exponential function to them. That explains why Mathematica produces such
a weird result - which by the way, doesn't coincide with what I get:

In[1]:=
data
= {{50, 22}, {64, 62}, {78, 122}, {93, 269}, {107, 414}, {122, 507}, {136,
      597}};

In[2]:=
g = Fit[data, Exp[x], x]
Out[2]=
5.151397928273713*^-57*E^x

On the other hand, what you quote as the result obtained in Excel has no
bearing to reality, either. If

In[3]:=
c[x_] := 7.5*Exp[0.0034x]

then

In[4]:=
c /@ Transpose[data][[1]]
Out[4]=
{8.88979, 9.32317, 9.77769, 10.2893, 10.7909, 11.3555, 11.9091}

These are the values corresponding to the abscissas in "data". No
resemblance whatsoever to the observed data. Perhaps you should try another
model.

Tomas Garza
Mexico City
----- Original Message -----
From: "joe" <joe at wam.umd.edu>
To: mathgroup at smc.vnet.net
Subject: [mg28029] [mg27986] Exponential fit question.


> 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 ?
>
> Thanks.
> -Joseph.
>
>



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