Compare TGraphs from several ROOT files

Newbie
1

Hello,

I’m a root beginner, and I would like to ask for help with the following. I want to open two or several root files where I have stored TGraphs and compare them by drawing them on the same canvas. Could you please give me some advice or a basic code on how to do this? I appreciate the help.

Cheers,
Alex

2

To plot them together it’s better to use a TMultiGraph; something like:

  // do similarly for all files/graphs:
  TFile *f1 = new TFile("file1.root");
  TGraph *g1 = (TGraph*)f1->Get("graph1");  // supposing file1.root contains graph1
  // ... (f2, g2, etc.)

  // then add all graphs to a multigraph and draw it:
  TMultiGraph *mg = new TMultiGraph();
  mg->Add(g1);
  mg->Add(g2);
  // ...
  mg->Draw("Al*");

Drawing options here:
https://root.cern/doc/master/classTGraphPainter.html

3

Hi, thank you so much for your answer! I just have one more question. Unfortunately, when I try to run a macro I’m getting this error:

error: no matching member function for call to ‘Add’

mg->Add(“gr1”);

~~^

/usr/local/Cellar/root/6.26.06_1/include/root/TMultiGraph.h:53:22: note: candidate function not viable: no known conversion from ‘const char [4]’ to

‘TGraph *’ for 1st argument

virtual void Add(TGraph *graph, Option_t *chopt=“”);

I tried several solutions including the root suggestion, but none of them seems to work. Can you tell me if you see something? Thanks.

4

Sorry, there were extra quotes in Add (should be Add(g1) etc.); now it’s corrected.

5

Thanks again for your answer. I already tried that, but I’m getting:

*** Break *** segmentation violation

every time. I don’t know why.

6

It looks like your graph was not found in your file.
You can try: if (g...) mg->Add(g...);
Try also: rootls -l yourfile.root