SequentialLR

class torch.optim.lr_scheduler.SequentialLR(optimizer, schedulers, milestones, last_epoch=-1)

Contains a list of schedulers expected to be called sequentially during the optimization process.

Specifically, the schedulers will be called according to the milestone points, which should provide exact intervals by which each scheduler should 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.

Example

>>> # Assuming optimizer uses lr = 0.05 for all groups
>>> # lr = 0.005     if epoch == 0
>>> # lr = 0.005     if epoch == 1
>>> # lr = 0.005     if epoch == 2
>>> # ...
>>> # lr = 0.05      if epoch == 20
>>> # lr = 0.045     if epoch == 21
>>> # lr = 0.0405    if epoch == 22
>>> scheduler1 = ConstantLR(optimizer, factor=0.1, total_iters=20)
>>> scheduler2 = ExponentialLR(optimizer, gamma=0.9)
>>> scheduler = SequentialLR(
...     optimizer,
...     schedulers=[scheduler1, scheduler2],
...     milestones=[20],
... )
>>> for epoch in range(100):
>>>     train(...)
>>>     validate(...)
>>>     scheduler.step()

get_last_lr()

Get the most recent learning rates computed by this scheduler.

Returns

A list of learning rates with entries for each of the optimizer’s param_groups, with the same types as their group["lr"]s.

Return type

list[float | Tensor]

Note

The returned Tensors are copies, and never alias the optimizer’s group["lr"]s.

get_lr()

Compute the next learning rate for each of the optimizer’s param_groups.

Returns

A list of learning rates for each of the optimizer’s param_groups with the same types as their current group["lr"]s.

Return type

list[float | Tensor]

Note

If you’re trying to inspect the most recent learning rate, use get_last_lr() instead.

Note

The returned Tensors are copies, and never alias the optimizer’s group["lr"]s.

load_state_dict(state_dict)

Load the scheduler’s state.

Parameters

state_dict (dict) – scheduler state. Should be an object returned from a call to state_dict().

recursive_undo(sched=None)

Recursively undo any step performed by the initialisation of schedulers.

state_dict()

Return the state of the scheduler as a dict.

It contains an entry for every variable in self.__dict__ which is not the optimizer. The wrapped scheduler states will also be saved.

Return type

dict[str, Any]

step()

Perform a step.