TRatioPlot TH1/THStack instead of THStack/TH1 in ratio plot

ROOT
,
1

Dear ROOT developers,

In Dec 2017, this(TRatioPlot h1/h2 instead of h2/h1) was raised but I found no solution.
When one uses TRatioPlot with THStack the ratio plot only shows the THStack/TH1 value which in my case means MC/data. Is it possible to reciprocate this ratio in order to get data/MC instead?

Best regards,
Federico Diaz Capriles

ROOT Version: 6.10.04-x86_64-slc6-gcc62-opt

2

Do you have a small macro showing what we are talking about ?

3

Yeah, sorry. Here is what I am trying to do:
h_stack is MC added together as a THStack and h_data are the data points as a TH1F. These are projected from trees in root files.

TRatioPlot *rp = new TRatioPlot(h_stack, h_data, "pois");
rp->Draw();

Though this can be shown easily with the example given in the reference:

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();
   c1->Update();
}

When one draws the TRatioPlot, it will have the ratio of h1/h2 on the bottom pad. Now, if one wants to have h2/h1 instead, one can just do auto rp = new TRatioPlot(h2, h1); instead of what is shown above. However, TRatioPlot only accepts THStack as the first argument and can only show a THStack/TH1 ratio. I would like to have the ability to have a TH1/THStack ratio instead.

4

I see now. In fact the TRatioPlot constructor using THStack converts the stack to a regular sum of its containing histograms. So, as an easy workaround, you can do the same before constructing the TRatioplot and use the normal constructor using two TH1.

5

Alright. Thanks, I’ll do that.

6

Note that the constructor you are requesting makes sense.

7

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