Re: TF1::Fit

From: Rene Brun (Rene.Brun@cern.ch)
Date: Mon Jan 11 1999 - 14:17:20 MET


Faouzi Attallah wrote:
> 
> Hi Rooters,
> 
> I am fitting a histogram hyds with a gaussian according to :
> 
>      g = new TF1("g","gaus",gmin, gmax);
>      hyds->Fit("g","ER0");
>      g->GetParameters(par);
>      hyds->Draw() ;
> 
> I got the following on my root-command-screen
> 
>  FCN=66.6685 FROM MINOS     STATUS=PROBLEMS     1282 CALLS        1694
> TOTAL
>                      EDM=2.55251e-05    STRATEGY= 2      ERROR MATRIX
> ACCURATE
>   EXT PARAMETER                  PARABOLIC         MINOS ERRORS
>   NO.   NAME      VALUE            ERROR      NEGATIVE      POSITIVE
>    1  Constant     1.47776e+02   4.41311e+00  -3.80487e+00   3.80193e+00
>    2  Mean        -2.83708e-04   3.83873e-04  -3.99915e-04   3.99098e-04
>    3  Sigma        1.52598e-02   2.16818e-06
> 
> but on the graphics an information-window is appearing with the
> hist- parameters (I do believe) not the fit ones :
> 
>         hyds
>         Nent = 1600
>         Mean = -0.00539024
>         RMS = 0.14343
> 
> is it a bug ?
> 
> Faouzi

No, you must activate the display of the fit parameters.
You have two solutions:
 1- select item "Fit parameters" in teh canvas "Option" menu
 2- gStyle->SetOptFit(); //see doc in this routine for options

Rene Brun



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