Migration frequency and wait() feature

[sowuy]

Hi, I have read the chapter https://link.springer.com/chapter/10.1007/978-3-642-28789-3_7 on the generalized model island, it helped me to understand deeper but I am still confused on two aspects:

1. I though that migration between islands only happens at the end of evolution on each island but in the chapter referenced, on page 158, a section discusses the "migration interval" also called "migration frequency" that specifies the iterations the algorithm must perform before a migration can occur. Does it mean that, by default, migration happens at the end of island evolution BUT the user can specify another frequency ?
2. In most problems, we want to gather the final results from each island and compare them (especially in multiobjective schemes). To me, this translates to use the wait() function on the archipelago after all asynchronous evolutions have been performed. However I was told not to use this function to reduce the number of synchronization points. But how do you gather your results then for the final comparison ? You still have to wait that all threads are finished at the end of the day (but correct me if I am wrong). Or maybe it just depends on everyone's need ? People can use the asynchronous threads live and do something out of it in specific applications ?