Plotting a single point onto a TH2

Newbie
1

Hey all.
I have a TH2 plot and would like to specify only one point on the histogram,
This is what I tried but point didn’t print on the histogram.

  tfile->GetObject("h2_alphabo10", h2_alphabo10);//get histogram from file
  h2_alphabo10->Draw("colz");

  //create TGraph
  //plot on the same canvas
  	
  const int n = 1;
  Double_t alpha = -0.051;
  Double_t board = 40.863;
  TGraph *g = new TGraph(n,board,alpha);
  g->SetMarkerStyle(21);
  g->SetMarkerSize(5);
  g->SetMarkerColor(kViolet+2);
  g->Draw("Psame");

Can kindly assist me?

Cheers

2

It is much simpler:

void th2marker(){
   auto h2 = new TH2F("h2","h2",10,-10,10,10,-10,10);
   h2->Fill(0.,0.);
   h2->Draw("col");
   auto m = new TMarker(-6,0,20);
   m->Draw();
}
3

Couet,

Thank you. The fill(0.,0.), will it print the histogram on the canvas? And why did you use auto? I am getting the histogram from a file.
So just use TMarker rather than TGraph?

Cheers

4

The first 3 lines are just an example to make a plot … I do not have your data…
The important bit is:

   auto m = new TMarker(xpos, ypos, 20);
   m->Draw();
5

Couet,

Thank you so much. It worked well.
Cheers