11/2015

11/10/2015

The following script creates a tree file with branches filled with random data.

#include "TROOT.h"

#include "TFile.h"

#include "TTree.h"

#include "TBrowser.h"

#include "TH2.h"

#include "TRandom.h"

// This example is a variant of hsimple.C but using a TTree instead

// of a TNtuple . It shows :

// -how to fill a Tree with a few simple variables.

// -how to read this Tree

// -how to browse and analyze the Tree via the TBrowser and TTreeViewer

// This example can be run in many different ways:

// way1: .x tree1.C using the CINT interpreter

// way2: .x tree1.C++ using the automatic compiler interface

// way3: .L tree1.C or .L tree1.C++

// tree1()

// One can also run the write and read parts in two separate sessions.

// For example following one of the sessions above, one can start the session:

// .L tree1.C

// tree1r();

//

// Author: Rene Brun

void tree1w()

{

  //create a Tree file tree1.root

  //create the file, the Tree and a few branches

  TFile f("tree1.root","recreate");

  TTree t1("t1","a simple Tree with simple variables");

  Float_t px, py, pz;

  Double_t random;

  Int_t ev;

  t1.Branch ("px",&px,"px/F");

  t1.Branch ("py",&py,"py/F");

  t1.Branch ("pz",&pz,"pz/F");

  t1.Branch ("random",&random,"random/D");

  t1.Branch ("ev",&ev,"ev/I");

  //fill the tree

  for (Int_t i=0;i<10000;i++) {

    gRandom ->Rannor (px,py);

    pz = px*px + py*py;

    random = gRandom ->Rndm ();

    ev = i;

    t1.Fill();

  }