RooPlot SetMaximum and SetLogy

ROOT
1

I’m trying to plot a RooDataHist with a log-scale on the Y-axis and a specific Y-axis range. When I specify the range of the Y-axis and use SetLogy(), I get an error:

Error in THistPainter::PaintInit: Cannot set Y axis to log scale

Here’s a simplified version of my code:

#!/usr/bin/env python
from ROOT import *
ht=RooRealVar("ht","Scalar Sum of pT [GeV]",100,12000);
pseudoExp=TH1D("h0","h0",120,0,12000)

#Create a pseudo experiment from a flat distribution
r=TRandom3(0)
for bin in range(1,pseudoExp.GetNbinsX()+1):
    weight=r.PoissonD(1E5)
    pseudoExp.SetBinContent(bin,weight)
    pseudoExp.SetBinError(bin,sqrt(weight))

dh=RooDataHist("dh","Data Hist for HT",RooArgList(ht),pseudoExp)
c1 = TCanvas("c1","c1",1200,800);
c1.Divide(2,1);
c1.cd(1);
c1.GetPad(1).SetLogy()
htFrame = ht.frame(1500,4000);
htFrame.SetMinimum(0.1)
htFrame.SetMaximum(2E5)
dh.plotOn(htFrame)
htFrame.Draw()

There are two problems. The first is that, without using SetLogy(), the minimum and maximum are not set correctly. The second problem is that when I use SetLogy(), the error I showed above my code occurs.

Any help would be greatly appreciated. I know this works in C++, so I might just end up converting it. But I’d rather not have to rewrite the entire script.

2

I’m not familiar with RooFit, but it could be that your commands are properly written, but the canvas isn’t being updated. Try adding:

gPad.Modified()
gPad.Update()

Jean-François

3

Hello Jean-François,
I tried your suggestion, but unfortunately it did not fix the problem. However, I managed to discover a solution by plotting the data before setting the minimum and maximum, rather than after.

Thank you!

Brian Amadio