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Reference Guide
hsimple.py File Reference



Detailed Description

View in nbviewer Open in SWAN This program creates :

  • a one dimensional histogram
  • a two dimensional histogram
  • a profile histogram
  • a memory-resident ntuple

These objects are filled with some random numbers and saved on a file.

from ROOT import TCanvas, TFile, TProfile, TNtuple, TH1F, TH2F
from ROOT import gROOT, gBenchmark, gRandom, gSystem
import ctypes
# Create a new canvas, and customize it.
c1 = TCanvas( 'c1', 'Dynamic Filling Example', 200, 10, 700, 500 )
c1.SetFillColor( 42 )
c1.GetFrame().SetFillColor( 21 )
c1.GetFrame().SetBorderSize( 6 )
c1.GetFrame().SetBorderMode( -1 )
# Create a new ROOT binary machine independent file.
# Note that this file may contain any kind of ROOT objects, histograms,
# pictures, graphics objects, detector geometries, tracks, events, etc..
# This file is now becoming the current directory.
hfile = gROOT.FindObject( 'py-hsimple.root' )
if hfile:
hfile = TFile( 'py-hsimple.root', 'RECREATE', 'Demo ROOT file with histograms' )
# Create some histograms, a profile histogram and an ntuple
hpx = TH1F( 'hpx', 'This is the px distribution', 100, -4, 4 )
hpxpy = TH2F( 'hpxpy', 'py vs px', 40, -4, 4, 40, -4, 4 )
hprof = TProfile( 'hprof', 'Profile of pz versus px', 100, -4, 4, 0, 20 )
ntuple = TNtuple( 'ntuple', 'Demo ntuple', 'px:py:pz:random:i' )
# Set canvas/frame attributes.
hpx.SetFillColor( 48 )
gBenchmark.Start( 'hsimple' )
# Initialize random number generator.
rannor, rndm = gRandom.Rannor, gRandom.Rndm
# For speed, bind and cache the Fill member functions,
histos = [ 'hpx', 'hpxpy', 'hprof', 'ntuple' ]
for name in histos:
exec('%sFill = %s.Fill' % (name,name))
# Fill histograms randomly.
px_ref, py_ref = ctypes.c_double(), ctypes.c_double()
kUPDATE = 1000
for i in range( 25000 ):
# Generate random values. Use ctypes to pass doubles by reference
rannor( px_ref, py_ref )
# Retrieve the generated values
px = px_ref.value
py = py_ref.value
pz = px*px + py*py
random = rndm(1)
# Fill histograms.
hpx.Fill( px )
hpxpy.Fill( px, py )
hprof.Fill( px, pz )
ntuple.Fill( px, py, pz, random, i )
# Update display every kUPDATE events.
if i and i%kUPDATE == 0:
if i == kUPDATE:
if gSystem.ProcessEvents(): # allow user interrupt
# Destroy member functions cache.
for name in histos:
exec('del %sFill' % name)
del histos
gBenchmark.Show( 'hsimple' )
# Save all objects in this file.
hpx.SetFillColor( 0 )
hpx.SetFillColor( 48 )
# Note that the file is automatically closed when application terminates
# or when the file destructor is called.
Wim Lavrijsen, Enric Tejedor

Definition in file hsimple.py.

A simple TTree restricted to a list of float variables only.
Definition: TNtuple.h:28
c SetBorderSize(2)
2-D histogram with a float per channel (see TH1 documentation)}
Definition: TH2.h:251
h1 SetFillColor(kGreen)
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format.
Definition: TFile.h:54
Profile Histogram.
Definition: TProfile.h:32
The Canvas class.
Definition: TCanvas.h:23
1-D histogram with a float per channel (see TH1 documentation)}
Definition: TH1.h:575