Dear Lesly!
As you have some many questions in one go, it might be interessting
for your to have a look at the (really good) manual, which can be
found on http://root.cern.ch/root/RootDoc.html.
Additionally there are some tutorials installed on your system: just
copy $ROOTSYS/tutorials some where to your homedirectory and start
root. It will print some help message.
BTW, please write a subject to your mail next time, have a look at
http://root.cern.ch/root/roottalk/RoottalkRules.html for more infos.
> {
> // create an empty root file first
> TFile f("filename.root","new");
>
> // create a histogram by reading it from a tree
>
>
>
> TH1F *ne = new TH1F("ne", "Num electrons",80,0,20);
> TTree *fChain; //!pointer to the analyzed TTree or TChain
> Int_t fCurrent; //!current Tree number in a TChain
> Int_t NELE; //define the type of NELE (the name of a leave
> in the tree)
You have to loop the tree somewhere here:
for (int i=0; i<fChain.GetEntries();i++){
fChain->GetEntry(i);
> ne->Fill(NELE); //fill data from a tree to a histogram
}
> ne->Write(); //write the histogram into the empty root
> file
> created
>
> }
Greets
Michael
>
> However, the above commands give me the wrong histogram with only one
> entry (supposed to be 1000 entries) when I open the histogram with
> TBrowser.
>
> So is there any suggestion?
>
> Also, if I have created such histograms, how can I add, subtracte or
> multipy different histograms?
>
> Thnaks a million!
>
> Lesley
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