Add RootPrimaryGenerator sampler to celer-sim

stognini commented 2 months ago

This PR is a follow up on issue #1207 and adds the capability to sample primaries from an existing ROOT file with offloaded primaries generated by RootEventWriter

Main additions:

New RootEventSampler class, derived from EventReaderInterface
Expanded json input options. Now if a ROOT file with offloaded primaries is provided as event_file, a file_sampling_options struct can be used:
```
"event_file": "offloaded-primaries.root",
"file_sampling_options": {
  "num_events": 5,
  "num_merged": 1
},
```
If either of those numbers is 0, the RootEventReader is constructed and reads it on an event-by-event basis. If both numbers are positive, the RootEventSampler is constructed and will sample primaries as requested.

stognini commented 2 months ago

Currently RootPrimaryGenerator is in phys/, but maybe should be moved to io/ which is where RootEventWriter/Reader are?

stognini commented 1 month ago

The word clumped has an unpleasant feel to it

Totally agree. Somehow it felt like 'merged' was a bit off, and 'concatenated' was long... But I guess merged is fine.

celeritas-project / celeritas

Add RootPrimaryGenerator sampler to celer-sim #1228