fillrandom.py File Reference

Namespaces
	fillrandom

Detailed Description

Fill a 1-D histogram from a parametric function.

Original tutorial by Rene Brun.

from ROOT import TCanvas, TPad, TFormula, TF1, TPaveLabel, TH1F, TFile
from ROOT import gROOT, gBenchmark



c1 = TCanvas( 'c1', 'The FillRandom example', 200, 10, 700, 900 )
c1.SetFillColor( 18 )

pad1 = TPad( 'pad1', 'The pad with the function',  0.05, 0.50, 0.95, 0.95, 21 )
pad2 = TPad( 'pad2', 'The pad with the histogram', 0.05, 0.05, 0.95, 0.45, 21 )
pad1.Draw()
pad2.Draw()
pad1.cd()

gBenchmark.Start( 'fillrandom' )
#
# A function (any dimension) or a formula may reference
# an already defined formula
#
form1 = TFormula( 'form1', 'abs(sin(x)/x)' )
sqroot = TF1( 'sqroot', 'x*gaus(0) + [3]*form1', 0, 10 )
sqroot.SetParameters( 10, 4, 1, 20 )
pad1.SetGridx()
pad1.SetGridy()
pad1.GetFrame().SetFillColor( 42 )
pad1.GetFrame().SetBorderMode( -1 )
pad1.GetFrame().SetBorderSize( 5 )
sqroot.SetLineColor( 4 )
sqroot.SetLineWidth( 6 )
sqroot.Draw()
lfunction = TPaveLabel( 5, 39, 9.8, 46, 'The sqroot function' )
lfunction.SetFillColor( 41 )
lfunction.Draw()
c1.Update()

#
# Create a one dimensional histogram (one float per bin)
# and fill it following the distribution in function sqroot.
#
pad2.cd();
pad2.GetFrame().SetFillColor( 42 )
pad2.GetFrame().SetBorderMode( -1 )
pad2.GetFrame().SetBorderSize( 5 )
h1f = TH1F( 'h1f', 'Test random numbers', 200, 0, 10 )
h1f.SetFillColor( 45 )
h1f.FillRandom( 'sqroot', 10000 )
h1f.Draw()
c1.Update()
#
# Open a ROOT file and save the formula, function and histogram
#
myfile = TFile( 'py-fillrandom.root', 'RECREATE' )
form1.Write()
sqroot.Write()
h1f.Write()
myfile.Close()
gBenchmark.Show( 'fillrandom' )

Author

Alberto Ferro

Definition in file fillrandom.py.