Entries != integral when adding 2 rootfiles

ROOT
1

Hi,

I have noticed that after adding rootfiles either with hadd or with TChain I get entries != integral when plotting the different trees. In the individual rootfiles (before adding them) entries == integral. This is puzzling for me. Can sb help on this? Is there sth I have not understood correctly?

thanks in advance
eleni

2

Hi,

This is strange. Do you have a concrete example?

Philippe.

3

Hi Philippe,

You can find an example in the tmp/emountri in lxplus302 (emountri.root).

cheers
eleni

4

Hi,

I unable to read your directory (permission are too strict):

Philippe.

5

Sorry, forgot to change the priviledges… should be ok now.

cheers
eleni

6

Hi Eleni,

In the directory I see a single large root file. However I can’t reproduce your problem.

How do you ‘add’ the file? Which files? How do you assert that ‘entries != integral’? Which exact branch/plot? Which command do you use to load the tree and plot the data? How does the result differ from your expectation?

Cheers,
Philippe.

7

Hi Philippe,

This is indeed the merged file and it has been created by TChain. If you look for example the variable dsVx1VxApproximD0Mass just using a TBrowser, you will see that in the entries: 6.37 10^7 while in the integral: 5.39 10^7. I would expect that these 2 values are the same (since there is no weighting). Is there sth I do not understand?

cheers
eleni

8

Hi,

It is a problem of numerical precision, float are too small for the amount of data you have, you need to use double. You need to use a TH1D histogram rather than the default (TH1F) to get the right answer:h2 = new TH1D("h2","h2",100,0,6); CollectionTree->Draw("dsVx1VxApproximD0Mass>>h2");

Cheers,
Philippe.

9

This indeed solves the problem!

thanks a lot for clearing this out! :slight_smile:
eleni