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MathGroup Archive 2001

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Re: Can Fit give function coefficients?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31101] Re: Can Fit give function coefficients?
  • From: "Paul Lutus" <nospam at nosite.zzz>
  • Date: Wed, 10 Oct 2001 03:43:12 -0400 (EDT)
  • References: <9pu3u0$bc8$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"Brett Patterson" <bap at roe.ac.uk> wrote in message
news:9pu3u0$bc8$1 at smc.vnet.net...
> I have a set of functions that I wish to fit to some data.
> Is there a way to succinctly get Mathematica to give me
> the coefficients of these functions in the fit.
>
> For example, say I have
> f1[x_] := 2 x^2
> f2[x_] := 3 x^3
>
> Normally, if I say: Fit[data, {1, f1[x], f2[x]}, x]
> I get a result in the form: a1 + b1 x^2 + c1 x^3,
> but I want a result of the form: a2 + b2 f1[x] + c2 f1[x].
> In this case, a2 = a1, b2 = b1/2, and c2 = c1/3.
>
> Is this possible?

No AFAIK, because the numerical coefficients cannot refer to functions that
are not defined, as you are showing them. Why do you want this feature? If
you change the functions, the generated numerical coefficients lose all
meaning. If the functions' definitions are included (true by default), the
output is valid.

Fit[] provides a numerical solution, not a symbolic one. You are asking for
a symbolic representation of a numerical solution.

--
Paul Lutus
www.arachnoid.com





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