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Re: NonlinearModelFit and ParameterTable

  • To: mathgroup at smc.vnet.net
  • Subject: [mg106413] Re: [mg106359] NonlinearModelFit and ParameterTable
  • From: Darren Glosemeyer <darreng at wolfram.com>
  • Date: Mon, 11 Jan 2010 18:54:37 -0500 (EST)
  • References: <201001100830.DAA05542@smc.vnet.net>

Ktota wrote:
> mtest1[t_,ltime_]:=If [var1*(t+var2-qtime)>8000,Sum[If [var1*(tsum
> +var2-qtime)>8000,8000*(1-P),var1*(tsum+var2- qtime)*(1-P)],{tsum,t-
> ltime+1, t,1}],Max[{Sum[{var1*(tsum+var2- qtime)*(1-P)},{tsum,t-ltime
> +1, t,1}]},0]]/156000
>
>
> i optimize the model above with:
>
> parameter2=
>  NonlinearModelFit[ExpData, mtest1[t, ltime], {ltime},
>    t]
>
>
> which is perfectly fine...
>
> but as soon i want to see the ParameterTable or the
> ConfidenceIntervals by doing this:
>
> parameter2["ParameterTable"]
>
> I get the following error message:
>
> and this only happens if i want to fit for ltime.. parameters P and
> var1 are perfectly fine....
>
> In[374]:= parameter2["ParameterTable"]
> During evaluation of In[374]:= General::ivar: 9.125191604503259` is
> not a valid variable. >>
> During evaluation of In[374]:= General::ivar: 9.125191604503259` is
> not a valid variable. >>
> During evaluation of In[374]:= General::ivar: 9.125191604503259` is
> not a valid variable. >>
> During evaluation of In[374]:= General::stop: Further output of
> General::ivar will be suppressed during this calculation. >>
> Out[374]= $Aborted
>
> if i only want to see the result it gives me no error:
> In[370]:= parameter2["BestFitParameters"]
> Out[370]= {ltime->9.12519}
>
> hope somebody can help...as this drives me mad...
>
> thank you very much
>
>  NuKtoBi
>   

A working example would be needed to figure out what is happening. My 
best guess is that there is a problem with the model specification 
(Daniel and Bob mentioned a couple possible issues) or that this example 
runs into trouble computing derivatives of the model which are needed 
for standard errors and such. If it is trouble with derivatives, it may 
be a bug in need of fixing, but a full working example would be needed.

Darren Glosemeyer
Wolfram Research


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