[ROOT] TH2F::Fit

From: steven staelens (steven.staelens@rug.ac.be)
Date: Mon Mar 17 2003 - 15:32:26 MET 

        Hi guys,


I'm using ROOT for the analysis of my nuclear medicine Monte Carlo
simulations results.  Therefore I want to fit a twodimensional function
to a 2D histogram.  I therefore use the following code:

#include "TF2.h"
#include "TH2.h"

void fit2d(){
  TFile b("t4.root");

  Singles->Draw("PosZ:PosX>>hnew(18,0,180,20,-200,200)");

  TF2 *f2e = new TF2("f2e",
"([0]*(y+201))/([1]*(x^2+(y+201)^2))",-0.5,180.5,-201,201) ;

  f2e->SetParameters(1,1) ;

  hnew->Fit("f2e")   ;

  hnew->Draw("LEGO") ;

  f2e->Draw("LEGO same");
}

The result I get is not satisfactory however as I see that the maxima of
the histogram and the fit are put equal.  This is of course not the most
appropriate fit as can be seen from the attached gif.  The wireframe
plot is the data while the filled lego plot is the fit.

In fact I was wondering how I could change the criteria in TH2F::Fit to
optimalize my 2D fit, as I have the impression now that it is mainly
penalizing the maximum deviation.

Thanks in advance,

best regards,

Steven

S. Staelens
Ghent University
ELIS / Medisip
Proeftuinstraat 86
B-9000 Gent
tel. 0032 9 264 66 28
fax. 0032 9 264 66 18
email: Steven.Staelens@rug.ac.be
2dfit.gif

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