Additional LR scheduler: Exponential Decay & Step Decay

[maxxrox]

Would it be possible to add in exponential LR decay, plus a method to enter arbitrary LR and matching step counts akin to 0.05:20, 0.005:100, 0.0005 - meaning 0.05 for 20 steps, then 0.005 until completing step 100 (so +80 steps), etc.?

I believe the exponential decay should look similar to the below sample, but wasn't certain how to update the lr_scheduler_util(?) bits (Python is not my forte) to test:

def exp_decay(epoch):
   initial_lrate = 0.1
   k = 0.1
   lrate = initial_lrate * exp(-k*t)
   return lrate
lrate = LearningRateScheduler(exp_decay)