hsimple.py

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## \file
## \ingroup Tutorials
## \notebook -js
##  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.
##
## \macro_image
## \macro_code
##
## \author Wim Lavrijsen, Enric Tejedor
 
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.Close()
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.
gRandom.SetSeed()
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:
         hpx.Draw()
 
      c1.Modified()
      c1.Update()
 
      if gSystem.ProcessEvents():            # allow user interrupt
         break
 
# 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 )
hfile.Write()
hpx.SetFillColor( 48 )
c1.Modified()
c1.Update()
 
# Note that the file is automatically closed when application terminates
# or when the file destructor is called.