interval.
state_dict()
  Returns the state of the scaler as a "dict".  It contains five
  entries:

  * ""scale"" - a Python float containing the current scale

  * ""growth_factor"" - a Python float containing the current
    growth factor

  * ""backoff_factor"" - a Python float containing the current
    backoff factor

  * ""growth_interval"" - a Python int containing the current
    growth interval

  * ""_growth_tracker"" - a Python int containing the number of
    recent consecutive unskipped steps.

  If this instance is not enabled, returns an empty dict.

  Note:

    If you wish to checkpoint the scaler's state after a
    particular iteration, "state_dict()" should be called after
    "update()".

step(optimizer, args, *kwargs)
  "step()" carries out the following two operations:

  1. Internally invokes "unscale_(optimizer)" (unless "unscale_()"
     was explicitly called for "optimizer" earlier in the
