Fill a TTree branch with TVector3

ROOT
1

Hi Rooters,

I am trying to fill a branch with an array of TVector3, however it appears that the branch containing TVector3 has entries either 0 or some absurd values.

To reproduce the problem I have attached a simple macro.
Can anyone suggest how to do this ?

Thanks in advance,

Tapasi
tree_with_vector.C (484 Bytes)

2

The first problem is that if you define a:
t.Branch(“vector”, &vPosition, “vposition[5]”);
then ROOT thinks that this branch is a:
*Br 1 :vector : Float_t vposition[5] *
Note the “Float_t” instead of the desired “TVector3”. See the “==> Case A” in the TTree class description.

Try:
root [0] TFile *f = TFile::Open(“test.root”, “read”)
root [1] tree->Print()

I guess you would need a single branch with a std::vector ("==> Case E") or a TClonesArray(“TVector3”) ("==> Case D"), or you would need to create 5 different branches, one branch per each “vposition[i]” (5 * “==> Case C”). You should probably also make sure that “splitlevel = 0”.

Another problem is that you create your tree on the stack “TTree t(…);”, but you’d better create it on the heap “TTree *t = new TTree(…);” (note: do NOT delete your “t” tree manually, it will be automatically deleted when your ROOT file “f” is deleted).

Well, maybe Philippe has any better ideas.

3

Hi Coyete,
Thanks !!
According to your suggestion I changed the file. I want to have a TVcetor3 (e.g., position) for each trajectory and I was thinking to create only one branch (“vector”) for each track.
I know if I create a branch with “double position[trajno][3]”, I can access those positions for each track. Is not it possible to have one TVector3 corresponding to one track …same like the “number” branch is doing ? So that if I do

tree->Scan(“vector[2]”); it will give information for trajectory number 2.

Another thing, evenif the sub-branches created under TVector3, say fX, I can not access the values for the tracks except 1st one. Now fX[2] is same as fX[0] ??
tree_with_vector.C (657 Bytes)

4

The line:
t->Branch(“vector”,vPosition);
means that you will store a SINGLE object pointed by “vPosition” (i.e. ONLY the “vPosition[0]”, see the “==> Case C” in the TTree class description).

5

Hi Coyete,
A related question to your second reply, when should I mention the “splitlevel=0” in the branch specifically to avoid memory problem ?

This is not clear to me.

Thanks in advance,

6

What “memory problem” do you mean?

7

In my code there are several TTree branches with “std::vector<vector>” and 2D arrays for each track and while creating the branches “splitlevel=0” is not mentioned.

And there is memory leak and it seems to me that the source is not pointer.

Those branches can be a reason for memory leak ??

8

In general, the “splitlevel” should not create memory leaks (it’s related to the way the objects are stored in the ROOT file).
Setting “splitlevel=0” prevents sometimes problems related to “subbranches with identical names” (another way is to add a “.” character at the ends of the names of their master branches).
See ROOT User’s Guide - Chapter 12. Trees - Adding a TBranch to Hold an Object and TTree::Branch.