ratioplot1.py

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## \file
## \ingroup tutorial_hist
## \notebook
## Example creating a simple ratio plot of two histograms using the `pois` division option.
## Two histograms are set up and filled with random numbers. The constructor of `TRatioPlot`
## takes the to histograms, name and title for the object, drawing options for the histograms (`hist` and `E` in this case)
## and a drawing option for the output graph.
## Inspired by the tutorial of Paul Gessinger.
##
## \macro_image
## \macro_code
##
## \author Alberto Ferro

import ROOT

ROOT.gStyle.SetOptStat(0)

c1 = ROOT.TCanvas("c1", "A ratio example")
h1 = ROOT.TH1D("h1", "h1", 50, 0, 10)
h2 = ROOT.TH1D("h2", "h2", 50, 0, 10)
f1 = ROOT.TF1("f1", "exp(- x/[0] )")
f1.SetParameter(0,3)

h1.FillRandom("f1",1900)
h2.FillRandom("f1", 2000)
h1.Sumw2()
h2.Scale(1.9/2.)

h1.GetXaxis().SetTitle("x")
h1.GetYaxis().SetTitle("y")

rp = ROOT.TRatioPlot(h1,h2)

c1.SetTicks(0,1)
rp.GetLowYaxis().SetNdivisions(505)
c1.Update()
c1.Draw()
rp.Draw()