Problems with setting the range of TGraph/TMultigraph

ROOT
1

Hi ROOT-team,

I’ve got some code producing graphs and putting them into a multigraph. In principle it works well, but I have some problems with setting the range of the x-axis.

I’ve attached the C-macro saved from the canvas, one gif-file with the un-zoomed output and one with my try to set the range of the x-axis from 0 to 20. I tried changing the ranges by hand on the canvas and with SetUserRange.

As you can see, the lower bound is around -50 instead of 0 and the higher bound is around 50 as well.

What do I have to do to change the ranges to for example 0 - 20?

thanks,

2

Example:

{
   TGraph *g[3];
   Double_t x[10] = {0,1,2,3,4,5,6,7,8,9};
   Double_t y[10] = {1,2,3,4,5,5,4,3,2,1};
   TMultiGraph *mg = new TMultiGraph();
   for (int i=0; i<3; i++) {
      g[i] = new TGraph(10, x, y);
      g[i]->SetMarkerStyle(20);
      g[i]->SetMarkerColor(i+2);
      for (int j=0; j<10; j++) y[j] = y[j]+1;
      mg->Add(g[i]);
   }
   mg->Draw("AP");
   mg->GetXaxis()->SetTitle("E_{#gamma} (GeV)");
   mg->GetYaxis()->SetTitle("Coefficients");

   gPad->Modified();
   mg->GetXaxis()->SetRange(29,65);
}
3

In the example you posted it works as I would expect. But what’s the reason it doesn’t work in my real-life application?

I added the line
multigraph->GetXaxis()->SetRange(5,6);
to the C-macro i’ve attached before and still don’t get any closer to the zoom-level I want (see attachment).

It seems to me, that I have to increase the number of bins somehow… but I’m drawing graphs, not histograms, so why do I have to care about bins anyway?

thanks,

4

do:

   multigraph->GetXaxis()->SetLimits(0.,20.);
5

This solves the problem.

Thanks

  • Peter
6

Hi,
I was also trying to plot a graph and modify the range of the axes. I tried with ‘->SetLimits(#,#)’, ‘->SetRange(#,#)’ as well as ‘->SetRangeUser(#,#)’. Nothing worked. I also referred to the pages Page1 and Page2. I have also tried as is advised here. But with no effect. My code is attached below. Any help will be appreciated.
MyGraph.C (1.6 KB)

Regards,
Saumyen

7

Can you provide something we can run ? the data file is missing

Also, for next time, avoid to reuse old posts … create a new one …
This one is 10 years old !

8

Try:

   multigraph->Draw("AP");
   gPad->Modified(); gPad->Update();
   multigraph->GetXaxis()->SetLimits(240., 3210.);
   multigraph->SetMinimum(-1.);
   multigraph->SetMaximum(33.);
   gPad->Modified(); gPad->Update();
9

Sorry Olivier, actually I was looking for solution and found this post to be on the same issue. Thought it’s better that I don’t open another post. Sorry!

10

Thanks a lot Wile (or, whatever-the-real-name-is :yum:) . It’s working fine. But I was wondering why the command multigraph->GetXaxis()->SetLimits(240., 3210.); is not working. Can you explain a bit, please?
Anyway, thank you again.

Regards,
Saumyen

11

I think this command is working … see Wile example.

12

Yeah, extremely sorry… I actually meant to say for the Yaxis, i.e., the command : multigraph->GetXaxis()->SetLimits(240., 3210.);.

Regards,
Saumyen

13

The Y axis’ limits for 1D histograms are defined by the min and max of the histogram,

14

Okay, I see. Thank you so much Olivier…