This function dispatches to either full_crossover() or
migration_crossover() depending on the which argument.
crossover(which, ...)A list with the following components:
new_prms_across_chains: The updated parameter matrix of shape p × n.
new_pis_across_chains: The updated vector of log-posterior values.
new_log_likes_across_chains: The updated vector of log-likelihood values.
character string, Either "diff" or "migration".
Further arguments passed to the underlying crossover function.