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Re: Help with an error with NonlinearModelFit, Mathematica 7.0

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99600] Re: Help with an error with NonlinearModelFit, Mathematica 7.0
  • From: dh <dh at metrohm.com>
  • Date: Fri, 8 May 2009 00:21:18 -0400 (EDT)
  • References: <gtudh6$it8$1@smc.vnet.net>


Hi,

ak^2 is interpreted as the square of ak, hardly what you want.

Here is an example:

=============================

a =.; b =.; c =.;

data = Table[{k, Log[a k^2 + b k + c]}, {k, 1, 50}] /. {a -> 1,

     b -> 2, c -> 3};

nlm = NonlinearModelFit[data, Log[a k^2 + b k + c], {a, b, c}, k]

=============================

Daniel



Anonymous wrote:

> I'm trying to find a fit to a large set of data.

> 

> Here are In[1], In[2].

> 

> In[1] := {{421.1, 6591.10}, ...};

> 

> (there are way more points, in fact there are 35 in total, but I don't

> want to list them.  All are real numbers.)

> 

> In[2] := nlm = NonlinearModelFit[data, Log[ak^2 + bk + c], {a,b,c}, k]

> 

> Then mathematica gives an error that basically says that the function

> "is not a list of real numbers"

> 

> Of course it is, so how do I fix this?

> 




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