Explicitly set error for TRatio plot

Newbie
1

Hi all, I am trying TRatioPlot recently, where I followed steps from ROOT: TRatioPlot Class Reference.
However it seems error bars is plotted for h1. What if I want to plot h2/h1 (reverse the arguments to TRatioPlot(h2,h1)), with the error bars for h1. Is there any method to explicitly set the plot style ? (something like HIST C options, but for individual histogram in the TRatioPlot)

void ratioplot1() {
   gStyle->SetOptStat(0);
   auto c1 = new TCanvas("c1", "A ratio example");
   auto h1 = new TH1D("h1", "h1", 50, 0, 10);
   auto h2 = new TH1D("h2", "h2", 50, 0, 10);
   auto f1 = new 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");
   auto rp = new TRatioPlot(h1, h2);
   c1->SetTicks(0, 1);
   rp->Draw();
   rp->GetLowYaxis()->SetNdivisions(505);
}

Thanks in advance

_ROOT Version: 6.24 (PyROOT via conda)
_Platform:Centos7
_Compiler: gcc9

2 
auto rp = new TRatioPlot(h2, h1);
rp->SetH1DrawOpt("E");
rp->SetH2DrawOpt("HIST C");
1 Like
3

Thanks for your quick reply.
I have another question for you:
How to set auto scale on Y-axis for this TRatio (It can be done automatically with THStack, but how about for the TRatio) ?

4

I would suggest you put the histogram with the largest maximum in:

auto rp = new TRatioPlot(h1, h2);
6

That’s exactly my workaround before the post, and it produced an truncated plot like this:
image

However, what I want to achieve is a plot (lower peak histo) / (higher peak histo) that without being cut at the highest peak (on the upper panel) so I could get a ratio that is in [0,1].

7

If it is just about the plot, try:

rp->Draw(); // c1->Modified(); c1->Update();
rp->GetUpperRefYaxis()->SetRangeUser(0., 2500.);
1 Like
8

Or change the maximum of the 1st histogram

1 Like
9

Did you mean h1->SetMaximum(3000); ?

10

Yes for instance.

1 Like