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MathGroup Archive 1998

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NonLinearRegress question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg12860] NonLinearRegress question
  • From: Easan Siviniah <easan at mrl.ucsb.edu>
  • Date: Wed, 17 Jun 1998 00:28:03 -0400
  • Organization: University of California, Santa Barbara
  • Sender: owner-wri-mathgroup at wolfram.com

Hi folks,

I'm writing some data fitting code on Mathematica that uses the add-on
package
'NonLinearRegress'. However I'm currently stumped because the model I
use
for fitting involves the use of conditional 'Ifs'. It seems that
Mathematica does not recoginise such a function as numerical.
Does Anyone have an idea of how to get round this. I've included a
typical
but simplified example below.

In[1]      Clear[fun,t,x,y]
              fun[t_,x_,y_]:=If[t<10,t^2 x + Log[t] y, t^3 x + Log[t] y]

              data=Table[{t,N[fun[t,2,3]]},{t,1,21,2}] Out[1]
{{1,2.},{3,21.2958},{5,54.8283},{7,103.838},{9,168.592},{11,2669.19},{13,

    4401.69},{15,6758.12},{17,9834.5},{19,13726.8},{21,18531.1}}

In[2]       << Statistics`NonlinearFit`
                NonlinearRegress[data,
                N[func[t,a,b]] ,z, {{a,{-100,-101}},{b,{2,3}}},
                RegressionReport -> BestFitParameters,
                 Method->FindMinimum,
                ShowProgress -> True]

Out[2]  NonlinearRegress::"nonnum": "The model is not numerical at
(******)
             Check that all model parameters are included in the
parameter list.



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