Thank you for the answers.
I understand now that the calculation is correct. I just was confused that
it is possible to get the different means of the same histogram in the
same range. But if this feature is known it is not problem for my
analysis.
Best regards,
Andrei.
On Wed, 15 Sep 2004, Rene Brun wrote:
> Andrei,
>
> The results are exactly what I expected. As soon as you set a range,
> the mean is computed using the bin centers. In the particular case
> where you set the range to the first and last channel, one could however
> use the more precise algorithm, but this would be yet another case to
> explain!
>
> Rene Brun
>
> On
> Wed, 15 Sep 2004, Andrei Kuznetsov wrote:
>
> >
> > {
> > gROOT->Reset();
> > TCanvas *cr = new TCanvas("cr","Amplitude",200,10,800,600);
> > TH1D *h=new TH1D("Pixel","Pixel",13,0,13);
> > for(Int_t i=0;i<6;i++) h->Fill(10*gRandom->Rndm());
> > cout<<"Mean befor SetRange ="<<h->GetMean()<<endl;
> > h->GetXaxis()->SetRange(0,12);
> > cout<<"Mean after SetRange ="<<h->GetMean()<<endl;
> > h->Draw();
> > cr->Update();
> > cr->Pop();
> > }
> >
> > The changing of the mean confuses people a little bit.
> >
> > Best regards,
> > Andrei.
> >
> >
> > On Wed, 15 Sep 2004, Rene Brun wrote:
> >
> > > Andrei,
> > >
> > > The member fTsumwx is incremented in the TH1::Fill methods using the true
> > > value of the x coordinate. TH1::GetMean returns the mean using this value.
> > >
> > > However, when you zoom via TAxis::SetRange, ROOT recomputes the mean value
> > > using the bin contents and the center of each bin.
> > >
> > > I do not see any problems with this method. If you have evidence of the
> > > contrary, please send the shortest possible running script showing the
> > > problem.
> > >
> > > Rene Brun
> > >
> > > Andrei Kuznetsov wrote:
> > > >
> > > > Hello,
> > > >
> > > > it looks like ROOT calculates fTsumwx (and hence Mean of a histogram) in
> > > > TH1 incorrectly.
> > > >
> > > > But if you perform
> > > > your_histogram->GetXaxis()->SetRange(a,b);
> > > > after the filling (or "zoom" by hands) it works correctly.
> > > >
> > > > It looks likes in the first case it is not used the center of bin when
> > > > fTsumwx is calculated.
> > > >
> > > > Best regards,
> > > > Andrei.
> > >
> >
>
>
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