Raise friendly errors in case of `num_epochs` is less than `num_warmup_epochs` in CIFAR10 and Transformers examples

I was trying to benchmark torch.inference_mode vs torch.no_grad on CIFAR10 example, so I just wanted to run for 3 epochs and average the benchmarks, the default warmup epochs is 4, so the scheduler will raise this error, which is not very clear to new users

f"Milestones should be increasing integers, but given {pair[0]} is smaller "
ValueError: Milestones should be increasing integers, but given 291 is smaller than the previous milestone 388

So I suggest to check num_epochs vs num_warmup_epochs inside run method and raise more clear error message for the users.

[DebarshiChanda]

Hey @KickItLikeShika, I think adding an assertion can solve this issue. Can you assign this to me?

[KickItLikeShika]

Hey @himanshu007-creator, thanks a lot for showing interest, we have these 2 examples:

• https://github.com/pytorch/ignite/tree/master/examples/contrib/cifar10
• https://github.com/pytorch/ignite/tree/master/examples/contrib/transformers

in both, if the num_epochs is less the num_warmup_epochs, the error in the description will be raised, we want to check inside the run method in both examples, if num_epochs is less than num_warmupds_epochs we should raise a friendly error message explaining what’s the error and why, and what the user should do (either increase the num_epochs or decrease num_warmup_epochs)