Using TGraph object as Parameter

[jedori0228]

Hi! In our input MC rootfile, we are saving TGraph objects into the TTree;

*............................................................................*
*Br  138 :ZExpA1CCQE : TGraph                                                *
*Entries :     1632 : Total  Size=     405032 bytes  File Size  =      35914 *
*Baskets :       13 : Basket Size=      32000 bytes  Compression=  11.26     *
*............................................................................*

This object is an event-by-event reweights (i.e., a TGraph where x:sigmas, y:reweights) and we use this dial with a Parameter definition as follows:

- parameterName: "ZExpA1CCQE"
  isEnabled: true
  dialSetDefinitions:
    - dialType: Graph
      minimumGraphResponse: 0
      dialLeafName: "ZExpA1CCQE"

When I run gundamFitter, we saw an error message:

libc++abi: terminating due to uncaught exception of type std::runtime_error: GenericToolbox::BranchBuffer::buildBuffer(): empty buffer size for branch: ZExpA1CCQE

After tracking down the source of the error, I found that in cpp-generic-toolbox/include/GenericToolbox.Root.h#L1531, the Leaf of this Branch has l->GetNdata() = 1 and l->GetLenType() = 0, thus got bufferSize = 0. In our on-going analysis, we put this TGraph into a TClonesArray, and there I saw the Leaf got l->GetNdata() = 0 and l->GetLenType() = 4, then had no issue. We can keep using TClonesArray, but wonder if using TGraph (or TSpline3) directly without TClonesArray can be also supported, or our configuration needs to be updated.

• GUNDAM tag: 1.9.0
• ROOT version: 6.30/06
• OS: osX 14.4

[nadrino]

Hello Jaesung! (Nice to meet you!)

What is the type of TObject you put in the TTree for ZExpA1CCQE?

[jedori0228]

Below is what we are basically doing:

    TGraph *gr = nullptr;
    theTree.Branch( "ZExpA1CCQE", &gr );

[nadrino]

Ok I see 🤔

We are actually using l->GetNdata() to figure out whether or not we should use an extended buffer for non-primitive objects. TClonesArray or TSpline3 typically return 0 here.

You could try to use TClonesArray in the meantime

[jedori0228]

I also tested saving TSpline instead, but getting same error. TTree print out is:

*............................................................................*
*Br  138 :ZExpA1CCQE : TSpline3                                              *
*Entries :     1627 : Total  Size=     974351 bytes  File Size  =     155105 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   6.28     *
*............................................................................*

, and also seeing

[JSKIMDEBUG][BranchBuffer::buildBuffer] _branchPtr_->GetName() = ZExpA1CCQE
[JSKIMDEBUG][BranchBuffer::buildBuffer] - nLeaves = 1
[JSKIMDEBUG][BranchBuffer::buildBuffer]   - iLeaf = 0
[JSKIMDEBUG][BranchBuffer::buildBuffer]     - l->GetNdata() = 1
[JSKIMDEBUG][BranchBuffer::buildBuffer]     - l->GetLenType() = 0

[nadrino]

Thank you very much @jedori0228

It seems like we need a new way to find out if a leaf is a TObject. TClonesArray should still work fine (we are actively using it for event-by-event dials).