hsum.py

#
# To see the output of this macro, click begin_html <a href="gif/hsum.gif" >here</a> end_html
#    Simple example illustrating how to use the C++ interpreter	
#    to fill histograms in a loop and show the graphics results
#

from ROOT import TCanvas, TH1F, TSlider
from ROOT import gROOT, gBenchmark, gRandom


gROOT.Reset();

# Create a new canvas, and customize it.
c1 = TCanvas( 'c1', 'The HSUM example', 200, 10, 600, 400 )
c1.SetGrid();

gBenchmark.Start( 'hsum' )

# Create some histograms.
total  = TH1F( 'total', 'This is the total distribution', 100, -4, 4 )
main   = TH1F( 'main', 'Main contributor', 100, -4, 4 )
s1     = TH1F( 's1', 'This is the first signal', 100, -4, 4 )
s2     = TH1F( 's2', 'This is the second signal', 100, -4, 4 )
total.Sumw2()   # this makes sure that the sum of squares of weights will be stored

# Set canvas/frame attributes.
total.SetMarkerStyle( 21 )
total.SetMarkerSize( 0.7 )
main.SetFillColor( 16 )
s1.SetFillColor( 42 )
s2.SetFillColor( 46 )

# Initialize random number generator.
gRandom.SetSeed()
gauss, landau = gRandom.Gaus, gRandom.Landau

# for speed, bind and cache the Fill member functions
histos = [ 'total', 'main', 's1', 's2' ]
for name in histos:
   exec '%sFill = %s.Fill' % (name,name)

# Fill histograms randomly
kUPDATE = 500
for i in xrange( 10000 ):
 # Generate random values.
   xmain = gauss( -1, 1.5 )
   xs1   = gauss( -0.5, 0.5 )
   xs2   = landau( 1, 0.15 )
   mainFill( xmain )

 # Fill histograms.
   s1Fill( xs1, 0.3 )
   s2Fill( xs2, 0.2 )
   totalFill( xmain )
   totalFill( xs1, 0.3 )
   totalFill( xs2, 0.2 )

 # Update display every kUPDATE events.
   if i and (i%kUPDATE) == 0 :
      if i == kUPDATE :
         total.Draw( 'e1p' )
         main.Draw( 'same' )
         s1.Draw( 'same' )
         s2.Draw( 'same' )
         c1.Update()
         slider = TSlider( 'slider', 'test', 4.2, 0, 4.6, total.GetMaximum(), 38 )
         slider.SetFillColor( 46 )

      if slider:
         slider.SetRange( 0, float(i) / 10000. )

      c1.Modified()
      c1.Update()

# Destroy member functions cache.
for name in histos:
   exec 'del %sFill' % name
del histos

# Done, finalized and trigger an update.
slider.SetRange( 0, 1 )
total.Draw( 'sameaxis' ) # to redraw axis hidden by the fill area
c1.Modified()
c1.Update()

gBenchmark.Show( 'hsum' )