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Re: naive question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg92818] Re: naive question
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Tue, 14 Oct 2008 04:56:47 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <gcv7ku$e63$1@smc.vnet.net>

Francisco Gutierrez wrote:

> I am using Fit within a function, and I want it to produce only a list of
>  coefficients, without the variables.
> For example, if I plug into fit the following: Fit[{{1,2,3},{4,5,6},{7,8,9}},{1,x1,x2},{x1,x2}],
> Mathematica produces:
> 1.55556+0.555556 x1+0.444444 x2
>  
> I want to get only the following list:
> {1.55556,0.555556,0.444444}
>  
> It seem awfully simple, but I haven't managed.
> How can I do it?

Arguably, the easiest way would be to use *FindFit* as follows:

In[1]:= {a, b, c} /.
  FindFit[{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}},
   a + b x1 + c x2, {a, b, c}, {x1, x2}]

Out[1]= {1.55556, 0.555556, 0.444444}

*FindFit* returns a list of replacement rules that are applied to the 
parameter names. (Note that the syntax for *FindFit* is slightly 
different from the syntax for *Fit*.)

Regards,
-- Jean-Marc


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