# LambdaLR

Source: https://www.tensorplay.cn/docs/generated/tensorplay.optim.lr_scheduler.LambdaLR.html

# LambdaLR

class tensorplay.optim.lr_scheduler.LambdaLR(optimizer: [Optimizer](tensorplay.optim.optimizer.Optimizer.html#tensorplay.optim.optimizer.Optimizer), lr_lambda: Callable[[[int](https://docs.python.org/3/library/functions.html#int)], [float](https://docs.python.org/3/library/functions.html#float)] | [list](https://docs.python.org/3/library/stdtypes.html#list)[Callable[[[int](https://docs.python.org/3/library/functions.html#int)], [float](https://docs.python.org/3/library/functions.html#float)]], last_epoch: [int](https://docs.python.org/3/library/functions.html#int) = -1)[[source]](../_modules/tensorplay/optim/lr_scheduler.html#LambdaLR)

Sets the initial learning rate.

The learning rate of each parameter group is set to the initial lr
times a given function. When last_epoch=-1, sets initial lr as lr.

Parameters:

- optimizer ([Optimizer](tensorplay.optim.optimizer.Optimizer.html#tensorplay.optim.optimizer.Optimizer)) – Wrapped optimizer.

- lr_lambda ( function or [list](https://docs.python.org/3/library/stdtypes.html#list)) – A function which computes a multiplicative factor given an integer parameter epoch, or a list of such functions, one for each group in optimizer.param_groups.

- last_epoch ([int](https://docs.python.org/3/library/functions.html#int)) – The index of last epoch. Default: -1.

Example

```
>>> # xdoctest: +SKIP
>>> # Assuming optimizer has two groups.
>>> num_epochs = 100
>>> lambda1 = lambda epoch: epoch // 30
>>> lambda2 = lambda epoch: 0.95**epoch
>>> scheduler = LambdaLR(optimizer, lr_lambda=[lambda1, lambda2])
>>> for epoch in range(num_epochs):
>>>     train(...)
>>>     validate(...)
>>>     scheduler.step()
>>>
>>> # Alternatively, you can use a single lambda function for all groups.
>>> scheduler = LambdaLR(opt, lr_lambda=lambda epoch: epoch // 30)
>>> for epoch in range(num_epochs):
>>>     train(...)
>>>     validate(...)
>>>     scheduler.step()
```

get_last_lr() → [list](https://docs.python.org/3/library/stdtypes.html#list)[[float](https://docs.python.org/3/library/functions.html#float) | TensorBase]

Get the most recent learning rates computed by this scheduler.

Returns:

A [list](https://docs.python.org/3/library/stdtypes.html#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](https://docs.python.org/3/library/stdtypes.html#list)[[float](https://docs.python.org/3/library/functions.html#float) | Tensor]

Note

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

get_lr() → [list](https://docs.python.org/3/library/stdtypes.html#list)[[float](https://docs.python.org/3/library/functions.html#float) | TensorBase][[source]](../_modules/tensorplay/optim/lr_scheduler.html#LambdaLR.get_lr)

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

Scales the base_lrs by the outputs of the lr_lambdas at
last_epoch.

Returns:

A [list](https://docs.python.org/3/library/stdtypes.html#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](https://docs.python.org/3/library/stdtypes.html#list)[[float](https://docs.python.org/3/library/functions.html#float) | Tensor]

Note

If you’re trying to inspect the most recent learning rate, use
[get_last_lr()](#tensorplay.optim.lr_scheduler.LambdaLR.get_last_lr) instead.

Note

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

load_state_dict(state_dict: [dict](https://docs.python.org/3/library/stdtypes.html#dict)[[str](https://docs.python.org/3/library/stdtypes.html#str), [Any](https://docs.python.org/3/library/typing.html#typing.Any)]) → [None](https://docs.python.org/3/library/constants.html#None)[[source]](../_modules/tensorplay/optim/lr_scheduler.html#LambdaLR.load_state_dict)

Load the scheduler’s state.

When saving or loading the scheduler, please make sure to also save or load the state of the optimizer.

Parameters:

state_dict ([dict](https://docs.python.org/3/library/stdtypes.html#dict)) – scheduler state. Should be an object returned
from a call to [state_dict()](#tensorplay.optim.lr_scheduler.LambdaLR.state_dict).

state_dict() → [dict](https://docs.python.org/3/library/stdtypes.html#dict)[[str](https://docs.python.org/3/library/stdtypes.html#str), [Any](https://docs.python.org/3/library/typing.html#typing.Any)][[source]](../_modules/tensorplay/optim/lr_scheduler.html#LambdaLR.state_dict)

Return the state of the scheduler as a [dict](https://docs.python.org/3/library/stdtypes.html#dict).

It contains an entry for every variable in self.__dict__ which is not the optimizer.
The learning rate lambda functions will only be saved if they are callable objects
and not if they are functions or lambdas.

When saving or loading the scheduler, please make sure to also save or load the state of the optimizer.

step(epoch: [int](https://docs.python.org/3/library/functions.html#int) | [None](https://docs.python.org/3/library/constants.html#None) = None) → [None](https://docs.python.org/3/library/constants.html#None)

Step the scheduler.

Parameters:

epoch ([int](https://docs.python.org/3/library/functions.html#int), optional) – 
Deprecated since version 1.4: If provided, sets last_epoch to epoch and uses
_get_closed_form_lr() if it is available. This is not
universally supported. Use [step()](#tensorplay.optim.lr_scheduler.LambdaLR.step) without arguments
instead.

Note

Call this method after calling the optimizer’s
step().