strange behavior for `intersection`

Hi @frheault and trx team,

I was working on the migration of validate_tractogram to DIPY (trying to understand the logic) and it seems that the option remove_identical_streamlines is not working as expected.

Looking deeper, it seems that intersection ignore flipped streamline. here an exemple:

arr = np.arange(90).reshape((30, 3))
stream = [np.flipud(arr), arr]
stream2 = [arr + 1, np.flipud(arr) + 1]

res, indices_uniq = perform_streamlines_operation(intersection, [stream, stream2])

I was expecting some results but I got ([], array([], dtype=uint32))

I do not understand anymore why I got a result when I do res, indices_uniq = perform_streamlines_operation(intersection, [stream])

Why the input should be a list of tractogram and not just one tractogram? (concatenate tractogram could be use if people want multiple tractogram in one).

Thank you in advance for the clarification

Reproduce the snippet with perform_streamlines_operation and intersection, then inspect how the operation handles one versus multiple tractograms and flipped streamlines. Done means the expected behavior is established and the implementation or its tests consistently reflect that behavior.