Adding histograms

ROOT
1

Hi,
I have added five histograms with the command h1->Add(h2) and so on for all five histo’s. The resulting histogram has very few counts. The original histograms each have something like 10^7 counts in total, while the resulting one has only about fifty thousand, but the histogram somehow seems to have the correct “shape”. Does anyone know what is happening? I could not find anything about this in the manual…

2

Could you send the shortest possible RUNNING script showing the problem?

Rene

3

Sure,
See the attached script and the input files and the resulting output file (I could not add the last file I merged with the other, but I guess the four others should give an idea).

I am running v. 5.18 on scientific linux for CERN.
cloverh4.root (16 KB)
cloverh3.root (17.8 KB)
cloverh2.root (17.8 KB)
cloverh1.root (16.3 KB)
cloverh.root (16 KB)
mergefiles.C (4.36 KB)

4

Your 5 files contain all one TCanvas object named “c1”. Each TCanvas contains a TH1F object named “h19”.
In your loop over files, you should read the TCanvas object with

TCanvas *c1 = (TCanvas*)curfile->Get("c1"); then access the histogram in c1 with

TH1 *h = (TH1*)c1->GetPrimitive("h19");
Rene