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

From: Rene Brun (Rene.Brun@cern.ch)
Date: Fri Aug 08 2003 - 15:03:42 MEST


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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