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MathGroup Archive 2001

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Re: Can Fit give function coefficients?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31139] Re: Can Fit give function coefficients?
  • From: bap at roe.ac.uk (Brett Patterson)
  • Date: Sat, 13 Oct 2001 02:47:04 -0400 (EDT)
  • References: <9pu3u0$bc8$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

I'd just like to summarise the feedback I've received so far,
since I think this thread is probably thinning out now.

Firstly, thank you everyone for responding to my question.

I have great suggestions in particular from:
Jens-Peer Kuska (kuska at informatik.uni-leipzig.de) --- using NumericQ
and BobHanlon at aol.com (BobHanlon at aol.com) --- using NonlinearFit.
Both are succinct and easy to implement, so I'm happy now! 8-)

I'd also like to share the following that I received via
private email from someone "Siegman" at Stanford:

> Here's a pointer to an expanded version of the standard  
> Fit[]  routine that 
> also gives the coefficients.
> 
>    http://www-ee.Stanford.EDU:80/~siegman/SimpleFit.txt

This SimpleFit function actually does exactly what I
was wanting, and it's fast!

Finally, thank for your help Yas, from Melbourne,
but for future reference, it's probably not a good
idea to post Notebooks as attachments to group lists.

Bye,
Brett Patterson


"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?
> 
> Regards,
> Brett Patterson


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