SequentialLR
class torch.optim.lr_scheduler.SequentialLR(optimizer, schedulers, milestones, last_epoch=- 1, verbose=False)
Receives the list of schedulers that is expected to be called
   sequentially during optimization process and milestone points that
   provides exact intervals to reflect which scheduler is supposed to
   be called at a given epoch.
Parameters:
      * optimizer (Optimizer) -- Wrapped optimizer.
  * **schedulers** (*list*) -- List of chained schedulers.

  * **milestones** (*list*) -- List of integers that reflects
    milestone points.

  * **last_epoch** (*int*) -- The index of last epoch. Default:
    -1.

  * **verbose** (*bool*) -- Does nothing.

-[ Example ]-



Assuming optimizer uses lr = 1. for all groups
lr = 0.1     if epoch == 0
lr = 0.1     if epoch == 1
lr = 0.9     if epoch == 2
lr = 0.81    if epoch == 3
lr = 0.729   if epoch == 4


