StepDecay

class paddle.optimizer.lr. StepDecay ( learning_rate, step_size, gamma=0.1, last_epoch=- 1, verbose=False ) [source]

Update the learning rate of optimizer by gamma every step_size number of epoch.

The algorithm can be described as the code below.

learning_rate = 0.5
step_size = 30
gamma = 0.1

learning_rate = 0.5     if epoch < 30
learning_rate = 0.05    if 30 <= epoch < 60
learning_rate = 0.005   if 60 <= epoch < 90
...
Parameters
  • learning_rate (float) – The initial learning rate. It is a python float number.

  • step_size (int) – the interval to update.

  • gamma (float, optional) – The Ratio that the learning rate will be reduced. new_lr = origin_lr * gamma . It should be less than 1.0. Default: 0.1.

  • last_epoch (int, optional) – The index of last epoch. Can be set to restart training. Default: -1, means initial learning rate.

  • verbose (bool, optional) – If True, prints a message to stdout for each update. Default: False .

Returns

StepDecay instance to schedule learning rate.

Examples

import paddle
import numpy as np

# train on default dynamic graph mode
linear = paddle.nn.Linear(10, 10)
scheduler = paddle.optimizer.lr.StepDecay(learning_rate=0.5, step_size=5, gamma=0.8, verbose=True)
sgd = paddle.optimizer.SGD(learning_rate=scheduler, parameters=linear.parameters())
for epoch in range(20):
    for batch_id in range(5):
        x = paddle.uniform([10, 10])
        out = linear(x)
        loss = paddle.mean(out)
        loss.backward()
        sgd.step()
        sgd.clear_gradients()
        scheduler.step()    # If you update learning rate each step
  # scheduler.step()        # If you update learning rate each epoch

# train on static graph mode
paddle.enable_static()
main_prog = paddle.static.Program()
start_prog = paddle.static.Program()
with paddle.static.program_guard(main_prog, start_prog):
    x = paddle.static.data(name='x', shape=[None, 4, 5])
    y = paddle.static.data(name='y', shape=[None, 4, 5])
    z = paddle.static.nn.fc(x, 100)
    loss = paddle.mean(z)
    scheduler = paddle.optimizer.lr.StepDecay(learning_rate=0.5, step_size=5, gamma=0.8, verbose=True)
    sgd = paddle.optimizer.SGD(learning_rate=scheduler)
    sgd.minimize(loss)

exe = paddle.static.Executor()
exe.run(start_prog)
for epoch in range(20):
    for batch_id in range(5):
        out = exe.run(
            main_prog,
            feed={
                'x': np.random.randn(3, 4, 5).astype('float32'),
                'y': np.random.randn(3, 4, 5).astype('float32')
            },
            fetch_list=loss.name)
        scheduler.step()    # If you update learning rate each step
  # scheduler.step()        # If you update learning rate each epoch
get_lr ( )

For those subclass who overload LRScheduler (Base Class), User should have a custom implementation of get_lr() .

Otherwise, an NotImplementedError exception will be thrown.

set_dict ( state_dict )

Loads the schedulers state.

set_state_dict ( state_dict )

Loads the schedulers state.

state_dict ( )

Returns the state of the scheduler as a dict.

It is a subset of self.__dict__ .

state_keys ( )

For those subclass who overload LRScheduler (Base Class). Acquiescently, “last_epoch, last_lr” will be saved by self.keys = ['last_epoch', 'last_lr'] .

last_epoch is the current epoch num, and last_lr is the current learning rate.

If you want to change the default behavior, you should have a custom implementation of _state_keys() to redefine self.keys .

step ( epoch=None )

step should be called after optimizer.step . It will update the learning rate in optimizer according to current epoch . The new learning rate will take effect on next optimizer.step .

Parameters

epoch (int, None) – specify current epoch. Default: None. Auto-increment from last_epoch=-1.

Returns

None