Stat box for TH2

ROOT
1

What does the overflow grid for TH2 exactly say?

E.g. my first example, the field in the middle shows the number of entries, but in my second example, it is a negative number (that hist goes from -150 to 150 on both axes). How should this be interpreted?

Thanks,

Andrea

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Screen Shot 2018-11-21 at 23.54.45.png800Ă—454 19.5 KB

ROOT Version: Not Provided
Platform: Not Provided
Compiler: Not Provided

2

Hi Andrea,
could you specify the type of your TH2:
TH2C, TH2I, TH2F or TH2D
You obviously have huge numbers.
Otto

3

Negative number for the number of entries is weird. Do you have a reproducer ?

4

Actually, negative numbers in the “underflows and overflows table” are possible if, for example, one uses negative “weights” when filling the histogram (but then I would also expect a negative “Integral”).
But this number is quite suspicious … 2147483648LL = 0x80000000 = -1L and so -2147483648LL = 0xffffffff80000000

5

Well it depends. see for instance the following lines:

root [0] TH1D *h = new TH1D("h","h",100,-1.,1)
root [1] h->Fill(0.,1.)
root [2] h->GetEntries()
(double) 1.0000000
root [3] h->Fill(0.,-1.)
root [4] h->GetEntries()
(double) 2.0000000
6

We are talking about the “number of overflows and underflows” table.

8

The histogram is TH2F. The weights are positive. I attached a file with the histogram.

Can you explain what does this mean?

histogram.root (18.9 KB)

9

Numerology

10

Your histogram has 9670702 entries and it then triggers a bug in the THistPainter::PaintStat2 method:

      if (h2->GetEntries() < 1e7)
         snprintf(t, 100," %7d|%7d|%7d\n", (Int_t)unov[3], (Int_t)unov[4], (Int_t)unov[5]);
      else
         snprintf(t, 100," %7d|%14.7g|%7d\n", (Int_t)unov[3], (Float_t)unov[4], (Int_t)unov[5]);

@couet The simplest fix would be to use:

      if (TMath::Abs(unov[4]) < 1.e7)

This bug is present in ROOT 5 and 6.

Note that this bug will also appear for another fields, as soon as they exceed the maximum value 2147483647 possible for an “(Int_t)”.

1 Like
11

@Wile_E_Coyote yes I was looking at that too.

12

@Wile_E_Coyote the fix you suggested is correct. I just pushed it in master.
Thanks !

13

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