Efficient way to load a 3D matrix and access randomly its vectorial field elements

[Javier_Galan]

Hi there,

I am just wondering if there inside ROOT a dedicated class to load a 3-dimensional matrix that defines 3-dimensional vectors. Thats it an object dedicated to host fieldmap-like data.

I am using the following approach

std::vector<std::vector<std::vector<TVector3>>> field;

but my matrix is of the order of 5M elements in total, So I have 5M TVector3 elements, and when I want to get those elements it starts to be a bit slow.

I though, perhaps using a TH3F for each of the field components would be more efficient?

Do you have any advice to improve performance here?

There is any 3-dimensional fieldmap-like class at ROOT that cares about the performance under the table?

[etejedor]

@moneta can perhaps give some advice on this? Thanks!

[moneta]

Hi,
Do you need to have the TVector3 functionality or just using the 3 coordinates ?
If you don’t need it, I would then use the RTensor class with 4 dimensions.
See https://root.cern.ch/doc/master/classTMVA_1_1Experimental_1_1RTensor.html

Lorenzo

[Javier_Galan]

@moneta

If you don’t need it, I would then use the RTensor class with 4 dimensions

Ok, thanks, that’s probably what we need.

We need to use certain TVector3 operations, but we could hardcode those if the gain in performance is worth.

[moneta]

You can probably store in memory the data in a RTensor or something similar (like a big std::vector ) and then re-fill a TVector3 when needed using for example
TVector3::SetXYZ( v1,v2,v3);

Lorenzo