TH2::Fill(const char *namex, const char *namey, Double_t w) doesn't update fTsumwxy

[YSelfTool]

This line:

root/hist/hist/src/TH2.cxx

Line 485 in 7aab9a2

fTsumwx2 += z * x * x;

Should be fTsumwxy += z * x * y; instead, as in the other versions TH2::Fill.
This was changed by 4465976, previously fTsumwxy was updated.

[lmoneta]

Hi,
That commit changed that behaviour on purpose, since there is no defined x and y value when the axis is alphanumeric. The bin centre corresponding to an arbitrary axes does not make sense.
What is your use case and why you need to have the histogram x and y statistics for the label case ?

[YSelfTool]

I don't need the axis statistics, I just think that incrementing fTsumwx2 twice in this function isn't correct.
It might be that the code in the if rarely happens and that if they are calculated the value is meaningless, but since the code to update the weighted axis sums exists, I would assume it should be the same as in all the other TH2::Fill functions and increment fTsum(w|w2|wx|wx2|wy|wy2|wxy) once each.
Currently, TH2::Fill with two bin names doesn't do that, instead it increments fTsumwx2 twice.
I'm sorry if I misunderstood the function, I just stumbled upon what seemed to be a typo when rebasing some other patches. If I'm wrong about this, please close the issue.

[lmoneta]

Ah I understand now, yes in the case the condition is true, fTsumwxy is not update.
This is certainly an error, I will make a PR fixing this.
Thank you for finding this out!

[guitargeek]

Actually fixed in 6.28.00, but that project didn't exist anymore on GitHub.