       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      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
{{1,2.},{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       << Statistics`NonlinearFit`
NonlinearRegress[data,
N[func[t,a,b]] ,z, {{a,{-100,-101}},{b,{2,3}}},
RegressionReport -> BestFitParameters,
Method->FindMinimum,
ShowProgress -> True]

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

```

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