Projecting underflow/overflow bins from TH3

ROOT
1

Usually the underflow/overflow bins are of no interest, but now I find myself wanting to project only them from a TH3. If I do the obvious thing and SetRange(0, 0) or SetRange(nbin+1, nbin+1) to get the underflow/overflow bin, this resets the axis range (as per the documentation).

So how can I do it without writing my own projection function?

Thanks in advance,

  • Peter
2

Hi,

This is a known limitation of Taxis::SetRange. You should do:

axis->SetRange(0,0);
axis->SetBit(TAxis::kAxisRange);

See Note 4 in root.cern.ch/root/htmldoc/TH3.html#TH3:Project3D

Regards

Lorenzo

3

I don’t want to exclude the overflow/underflow bins, I want to include them? Just as I can project any bin of a histogram out with SetRange(bin, bin), I want to project the underflow or overflow bin.

4

Hi,

yes you are right, for selecting ONLY underflow/oveflow it will not work !
We will need to fix Taxis::SetRange. In the meantime, you can Project using all range (including underflow and/or overflow) and then subtract the histogram projected excluding them.
This is still better than writing your own projection function

Lorenzo

5

Hi,

just wanted to comment that this issue is ATM fixed at least in the trunk version (e.g. will probably be available in root-6.X).