Re: [ROOT] what's with the fitters? can't get params or error matrix

From: Dr. John Krane (jkrane@netzero.com)
Date: Fri Aug 08 2003 - 15:23:10 MEST


Hi Rene,

Yesterday, I wrote my own fitter that has something very similar to what 
you added, but with one more method:

     virtual Double_t Get1Parameter(Int_t ipar);
     virtual Double_t Get1Error(Int_t ipar);
     virtual void     GetEMat(Double_t *emat, Int_t ndim);

I was just writing to you to tell you about it.  Anyway, a method to get 
a single error might be nice also.

Thanks very much for updating the classes!  I'm continually impressed 
with the responsiveness of all the ROOT authors/developers.

	- John

Rene Brun wrote:
> Hi  John,
> 
> I agree with your comments.
> I have extended TVirtualFitter (now in CVS), adding two new functions
>   Double_t* GetCovarianceMatrix
>   Double_t  GetParameter(int ipar)
> 
> Rene Brun
> 
> On Wed, 6 Aug 
> 2003, Dr. John Krane wrote:
> 
> 
>>Hi,
>>
>>I'm trying to get the final fit parameter values and the covariance 
>>matrix out of TVirtualFitter or TFitter.  Is there no way to do this?
>>
>>I see
>>
>>Int_t GetParameter(Int_t ipar,char *parname,Double_t &value,Double_t 
>>&verr,Double_t &vlow, Double_t &vhigh)
>>
>>...but this looks like a cut'n'paste of SetParameter.  Why would I have 
>>to provide the initial values just to get the current one?!  Should this 
>>not be
>>
>>Double_t GetParameter(Int_t ipar)
>>
>>...with a simple inline implementation?  There also appears to be *no 
>>way* to get the covariance matrix.  Perhaps I should have bypassed 
>>TVirtualFitter entirely and just used TMinuit directly.  This course 
>>seemed unwise to me at first, or at least non-aesthetic, but 
>>TVirtualFitter seems to lack even the basic functionality I need.
>>
>>If I am wrong, could somebody please tell me how to (for instance) 
>>modify the code of
>>
>>http://root.cern.ch/cgi-bin/print_hit_bold.pl/root/html/examples/minexam.cxx.html
>>
>>to get the parameters and covariance matrix with high-precision?  I am 
>>looking for something similar to mnemat for the latter.
>>
>>	- John
>>
> 
> 
> 
> 



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