Hepmc3 nightly fixes 26122020 part 1
In this MR, for the HepMC3 compatibility:
- Update the types, i.e.
GenParticle*
->GenParticlePtr
- Use C++11 loops
- Added some comments on the algorithm
Edited by Andrii Verbytskyi
In this MR, for the HepMC3 compatibility:
GenParticle*
-> GenParticlePtr