Requires large chunk of memory when having many sources

[martwo]

This lines brakes when using many sources (400+) due to large memory allocation of 20+GB. Maybe use int32 instead of int64!?

skyllh/skyllh/core/event_selection.py

Line 577 in e99102e

idxs = np.argwhere(mask_dec[:, mask])

[martwo]

It is not possible to specify the dtype of the resulting idxs array. Also np.nonzero(a) does not support to specify the dtype of the resulting array :( One might have to write a batched version of np.argwhere and batch chunks of sources.

[martwo]

The issue arises for the pre_event_selection_method of the background generation method, when O(10 million) MC events are selected for all the sources.