       Re: Exponetial Fit

• To: mathgroup at christensen.cybernetics.net
• Subject: [mg1823] Re: Exponetial Fit
• From: hsh104 at psu.edu (Hein Hundal)
• Date: Thu, 3 Aug 1995 23:52:06 -0400
• Organization: CAC

```In article <3ui5dj\$231 at news0.cybernetics.net> crunch at s-cwis.unomaha.edu (John L. White) writes:

>        I have tried to do a exponetial fit to a list of data from a physics
>experiment, but Mathematica does a terrible job when I do the following
>command:

>Exp[Fit[Log(data),{1,t},t]]

Depending on what you mean by an exponential fit, there are some better
ways.

If you want to find the best fit of the form y = A Exp[B x], try

logy[{x_,y_}] := {x, Log[y]}
logpoints = Map[logy, points] //N
Exp[Fit[logpoints, {1,x}, x]]

This gives the correct answer for

points = {{1, 3 Exp}, {2, 3 Exp}, {3, 3 Exp}}
(* f[x] = 3 Exp[2 x] *)

If you want to find the best fit of the form y = A x^B, try

logpoints = Map[logy, points] //N
Exp[Fit[logpoints, {1, Log[x]}, x]]

This gives the correct answer for

points = {{1, 3}, {2, 12}, {3, 27}, {4, 48}}
(* f[x] = 3 x^2 *)

I hope that helps.  - Hein Hundal

```

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