Problems to draw a weighted sum of histograms

From: Antonio Augusto Alves Junior <aalvesju_at_cern.ch>
Date: Tue, 26 Aug 2008 01:25:14 -0300

Hi all,

Please, can you help me?
I am using the TH1::Add(const TH1* , Double_t ) to add two histograms. I build the histogram h = c1*h1 + c2*h2, doing this

h->Reset();
h->Add( h1, c1);
h->Add(h2,c2);

here the h, h1 and h2 are TH1F objects, then I draw the histogram

h->Draw();

The problem:

In the generated graph, is still possible see contributions from h1 histogram when c1 is null!
By other side, the histogram's parameters, like h->Integral(), h->GetEntries() etc, has the correct values.

Some hint?

Hi all,

Please, can you help me?
I am using the TH1::Add(const TH1* , Double_t ) to add two histograms. I build the histogram h = c1*h1 + c2*h2, doing this

h->Reset();
h->Add( h1, c1);
h->Add(h2,c2);

here the h, h1 and h2 are TH1F objects, then I draw the histogram

h->Draw();

The problem: in the generated graph, is still possible see contributions from h1 histogram when c1 is null! By other side, the histogram's parameters, like h->Integral(), h->GetEntries() etc, has the correct values.

Some hint?

Hi all,

Please, can you help me?
I am using the TH1::Add(const TH1* , Double_t ) to add two histograms. I build the histogram h = c1*h1 + c2*h2, doing this

h->Reset();
h->Add( h1, c1);
h->Add(h2,c2);

here the h, h1 and h2 are TH1F objects, then I draw the histogram

h->Draw();

The problem: in the generated graph, is still possible see contributions from h1 histogram when c1 is null! By other side, the histogram's parameters, like h->Integral(), h->GetEntries() etc, has the correct values.

Some hint? Is it a bug in the Draw() method? The piece of code is below.

Best regards
Augusto

     vector.front()->chain->Draw(draw_opt, filter, "goff" );     TH1F *h = (TH1F*) (gDirectory->Get( histo_name ))->Clone("h");     h->Reset();
    Int_t h_nr=0;    

    for( ChainVector::const_iterator it_vector = vector.begin(); it_vector != vector.end(); it_vector++ )

    {

       
        TString  h_name("histo_");
        h_name += h_nr;
        h_nr++;
       
        (*it_vector)->chain->Draw(draw_opt, filter,  "goff" );
        TH1F *h1 = (TH1F*)(gDirectory->Get( histo_name ) ) 
        h->Add(h1, (*it_vector)->weight  );
        delete h1;  

    }    

    h->Draw(); Received on Tue Aug 26 2008 - 06:25:48 CEST