Re: Pythia and generated particles

Mario,

We already have many examples with TClonesArray in the tutorials. See, for instance: tcl.C, Jets.C, pythiaExample.C

Rene Brun

On Mon,
14 Feb 2005, 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 - 21:11:17 MET