Re: Bug in TTree::Project() ?

Rene Brun (Rene.Brun@cern.ch)
Wed, 03 Feb 1999 09:26:09 +0100

Dmitry Onoprienko wrote:
>
> When I use TTree::Project() function to fill a TH2F histogram, some data
> members
> (fTsumwy, fTsumwy2, fTsumwxy) are not calculated. As a result, some public
> functions (GetRMS(), GetCorrelationFactor(), ...) produce incorrect results.
> Using Draw() instead of Project() allows to avoid the problem.
>
> I'm running ROOT under Windows. Here is a test macro :
>
> {
> #include <iostream.h>
>
> c1 = new TCanvas("c1","Ntuple projection test",500,500);
>
> TFile *f = new TFile("test.root", "RECREATE");
>
> TNtuple *nt = new TNtuple("nt","test","x:y");
> TH2F *h = new TH2F("h","htitle",100,-4.,4.,100,-4.,4.);
>
> Float_t x,y;
> Int_t event = 500;
> TRandom rn = new TRandom();
> while (event-->0) {
> nt->Fill(rn.Gaus(),rn.Gaus());
> }
> f->Write();
>
> nt->Project("h","x:y");
> h->Draw();
> c1->Update();
> cerr << "Now check statistics for the displayed histogram\n";
> cerr << "Mean and RMS along Y are zero, also\n";
> cerr << "h->GetCorrelationFactor() gives " << h->GetCorrelationFactor()
> <<endl;
>
> }

Hi Dmitry,
Statistics for 2-d histograms were not filled by TTree::Draw.
I have fixed this problem in version 2.21/04
Thanks for reporting this problem.

Rene Brun