Implementation of ReduceLROnPlateau scheduler

[ahmedo42]

🚀 Feature

While there might be some workarounds in using ReduceLROnPlateau with ignite's optimizer , it would be nicer to have a standalone feature like other schedulers in contrib.

Relevant issue and code sample.

[sadra-barikbin]

Hi there,
I made this feature's PR. Is it OK? What else should I do?

[sdesrozis]

@ahmedo42 It exists the class LRScheduler to wrap PyTorch schedulers. Out of curiosity, have you tried it? And if so, why doesn't it work on this case? Thanks a lot for the feedback!

[sadra-barikbin]

@sdesrozis LRScheduler does not support param_group_index and also It's not sufficient to just wrap a PyTorch's ReduceOnPlateau, but one should also feed its step function with a metric value.