Re: Pythia and generated particles

From: Axel Naumann <axel-naumann_at_gmx.de>
Date: Mon, 14 Feb 2005 14:22:27 -0600

Hi Mario,
oops, I meant to answer your email, but forgot. There is already a similar tutorial on that, see
http://root.cern.ch/root/html/examples/eventa.cxx.html But it needs an update; I try to get that done. Axel.

Mario Kadastik wrote:

> Well I managed to get what I wanted. Namely:
> 
> TFile f("higgs.root");
> TTree *t = (TTree*)f.Get("particles");
> TClonesArray *part=0;
> TMCParticle *p=0;
> Int_t i=0,j=0;
> t->SetBranchAddress("particles",&part);
> for (i=0; i<t->GetEntries(); i++) {
>   t->GetEntry(i);
>   for (j=0;j<part->GetEntries();j++) {
>       p=(TMCParticle*)part->At(j);
>       // here p contains particle nr j from run i.
>       printf("Run: %d, Particle nr %d is %s\n",i,j,p->GetName());
>    }
> }
> 
> Maybe a similiar sample should be added to the tutorial/howto part?
> 
> Mario
> 
> Mario Kadastik wrote:
> 

>> Hello,
>>
>> It seems to me that I'm a bit stuck with Pythia and ROOT trees.
>>
>> Namely I saved the pythia generated particles as TCloneArrays into a
>> root file. If I open it up in TBrowser or scan it, then I can see all
>> the relevant data there. Now if I want to loop over the information,
>> then I'm stuck.
>>
>> What I'd like to do is to loop over all events and in every one of
>> them loop over all particles and do something. How should that be
>> accomplished? At the moment I'm having trouble reading the data out of
>> the tree in my code:
>>
>> TFile f("higgs.root")
>> TTree *t = (TTree*)f.Get("particles")
>> Float_t *px;
>> t->SetBranchAddress("particles.fPx",px)
>> t->GetEntry()
>> and after that px won't contain anything useful.
>>
>> If I swap Float_t *px with Float_t px[1000], no change.
>> I also tried to t->SetMakeClass(1) and the same with chains, but in
>> both cases I get segmentation fault I'm using latest root on Fedora
>> Core 3 (downloaded yesterday).

> 
> 
> 

Received on Mon Feb 14 2005 - 21:32:55 MET