TH2::Draw("col") after Eval(TF2 *)

ROOT
1

I am expecting a set of color rectangles for the following
script

{ h2 = new TH2D("h2", "h2", 10, -2, 2, 10, -2, 2); f2 = new TF2("f2", "1 - x*x - y*y", -2, 2, -2, 2); h2->Eval(f2); h2->Draw("col"); }but it produces an empty frame.

works fine. I can obtain the plot that I wish with

h2->Fill(0, 0, 0); h2->Draw("col");
Version info:
Linux i686 (Debian squeeze), ROOT 5.28.00a

Thanks in advance.

P.S. Sorry, I failed to report this issue as a bug due to
my internet povider is in the savannah blacklist.

2

The 2D representations of 2D histograms are painted in THistPainter::PaintTable()
which does the painting only if: fH->GetEntries() != 0
so if there is no entries nothing is painted.

3

Should I consider this as a feature?

4

It is implemented that way on purpose since the very beginning of ROOT. Changing it may have unwanted side effects. You can simply set the number of entries to 1 and it will work as you wish.

5

Thank you for the explanation, Olivier.