ratioplot.py File Reference

Namespaces
	ratioplot

Detailed Description

Display two histograms and their ratio.

This program illustrates how to plot two histograms and their ratio on the same canvas. Original macro by Olivier Couet.

from ROOT import TCanvas, TColor, TGaxis, TH1F, TPad
from ROOT import kBlack, kBlue, kRed


def createH1():
    h1 = TH1F("h1", ("Two gaussian plots and their ratio; x title; h1 and h2"
                " histograms"), 100, -5, 5)
    h1.SetLineColor(kBlue+1)
    h1.SetLineWidth(2)
    h1.FillRandom("gaus")
    h1.GetYaxis().SetTitleSize(20)
    h1.GetYaxis().SetTitleFont(43)
    h1.GetYaxis().SetTitleOffset(1.55)
    h1.SetStats(0)
    return h1


def createH2():
    h2 = TH1F("h2", "h2", 100, -5, 5)
    h2.FillRandom("gaus")
    h2.SetLineColor(kRed)
    h2.SetLineWidth(2)
    return h2


def createRatio(h1, h2):
    h3 = h1.Clone("h3")
    h3.SetLineColor(kBlack)
    h3.SetMarkerStyle(21)
    h3.SetTitle("")
    h3.SetMinimum(0.8)
    h3.SetMaximum(1.35)
    # Set up plot for markers and errors
    h3.Sumw2()
    h3.SetStats(0)
    h3.Divide(h2)

    # Adjust y-axis settings
    y = h3.GetYaxis()
    y.SetTitle("ratio h1/h2 ")
    y.SetNdivisions(505)
    y.SetTitleSize(20)
    y.SetTitleFont(43)
    y.SetTitleOffset(1.55)
    y.SetLabelFont(43)
    y.SetLabelSize(15)

    # Adjust x-axis settings
    x = h3.GetXaxis()
    x.SetTitleSize(20)
    x.SetTitleFont(43)
    x.SetTitleOffset(4.0)
    x.SetLabelFont(43)
    x.SetLabelSize(15)

    return h3


def createCanvasPads():
    c = TCanvas("c", "canvas", 800, 800)
    # Upper histogram plot is pad1
    pad1 = TPad("pad1", "pad1", 0, 0.3, 1, 1.0)
    pad1.SetBottomMargin(0)  # joins upper and lower plot
    pad1.SetGridx()
    pad1.Draw()
    # Lower ratio plot is pad2
    c.cd()  # returns to main canvas before defining pad2
    pad2 = TPad("pad2", "pad2", 0, 0.05, 1, 0.3)
    pad2.SetTopMargin(0)  # joins upper and lower plot
    pad2.SetBottomMargin(0.2)
    pad2.SetGridx()
    pad2.Draw()

    return c, pad1, pad2


def ratioplot():
    # create required parts
    h1 = createH1()
    h2 = createH2()
    h3 = createRatio(h1, h2)
    c, pad1, pad2 = createCanvasPads()

    # draw everything
    pad1.cd()
    h1.Draw()
    h2.Draw("same")
    # to avoid clipping the bottom zero, redraw a small axis
    h1.GetYaxis().SetLabelSize(0.0)
    axis = TGaxis(-5, 20, -5, 220, 20, 220, 510, "")
    axis.SetLabelFont(43)
    axis.SetLabelSize(15)
    axis.Draw()
    pad2.cd()
    h3.Draw("ep")

# To hold window open when running from command line
#  text = raw_input()


if __name__ == "__main__":
    ratioplot()

Author

Michael Moran

Definition in file ratioplot.py.