Bug in TH1::Merge

ROOT
1

I don’t know if I’m missing something, but I think somethings is wrong:

{
    TH1F h1;
    h1.Fill("10", 0);
    h1.Fill("20", 0);
    h1.Fill("30", 0);

    h1.Fill("10", 1);
    h1.Fill("10", 1);
    h1.Fill("10", 1);
    h1.Fill("20", 1);
    h1.Fill("30", 1);
    h1.SetName("h1");
    h1.Print("ALL");
    TCanvas c1("c1", "first"); h1.DrawCopy();
    cout << "X axis minimum: " << h1.GetXaxis()->GetXmin() << endl;

    
    TH1F h2;
    h2.Fill("10", 0);
    h2.Fill("20", 0);
    h2.Fill("30", 0);

    h2.Fill("10", 1);
    h2.Fill("20", 1);
    h2.Fill("20", 1);
    h2.Fill("30", 1);
    h2.SetName("h2");
    h2.Print("ALL");
    TCanvas c2("c2", "second"); h2.DrawCopy();
    cout << "X axis minimum: " << h2.GetXaxis()->GetXmin() << endl;


    TH1F h = h1;
    TObjArray l;
    l.Add(&h2);
    h.Merge(&l); // h.Add(&h1) works
    h.Print("ALL");
    cout << "X axis minimum: " << h.GetXaxis()->GetXmin() << endl;
    TCanvas c("sum", "sum"); h.DrawCopy();
}

I’m just Merging two TH1F, but the result is wrong! Result =

TH1.Print Name  = h1, Entries= 15, Total sum= 9
 fSumw[0]=0, x=-6
 fSumw[1]=5, x=-2
 fSumw[2]=3, x=2
 fSumw[3]=1, x=6
 fSumw[4]=0, x=10
 fSumw[5]=0, x=14
X axis minimum: -4

for example the first bin: 3+1 = 5?

2

I’m guessing if the problem is this: savannah.cern.ch/bugs/?75902

the point is that I’m using ROOT ROOT 5.28/00b (branches/v5-28-00-patches@38394, Mar 20 2011, 05:49:00 on linuxx8664gcc), but I don’t trust so much the splash screen because my TH1.cxx is different from the svn@38394 one.

3

Hi,

This bug has not been ported in the 5.28 patches, but it is has been fixed in the trunk since some time
(a couple of months)

Best Regards

Lorenzo