tf.keras.experimental.NoisyLinearCosineDecay

Class `NoisyLinearCosineDecay`

A LearningRateSchedule that uses a noisy linear cosine decay schedule.

Inherits From: LearningRateSchedule

Aliases:

`init`

__init__(
    initial_learning_rate,
    decay_steps,
    initial_variance=1.0,
    variance_decay=0.55,
    num_periods=0.5,
    alpha=0.0,
    beta=0.001,
    name=None
)

Applies noisy linear cosine decay to the learning rate.

See [Bello et al., ICML2017] Neural Optimizer Search with RL. https://arxiv.org/abs/1709.07417

For the idea of warm starts here controlled by num_periods, see [Loshchilov & Hutter, ICLR2016] SGDR: Stochastic Gradient Descent with Warm Restarts. https://arxiv.org/abs/1608.03983

Note that linear cosine decay is more aggressive than cosine decay and larger initial learning rates can typically be used.

When training a model, it is often recommended to lower the learning rate as the training progresses. This schedule applies a noisy linear cosine decay function to an optimizer step, given a provided initial learning rate. It requires a step value to compute the decayed learning rate. You can just pass a TensorFlow variable that you increment at each training step.

The schedule a 1-arg callable that produces a decayed learning rate when passed the current optimizer step. This can be useful for changing the learning rate value across different invocations of optimizer functions. It is computed as:

def decayed_learning_rate(step):
  step = min(step, decay_steps)
  linear_decay = (decay_steps - step) / decay_steps)
  cosine_decay = 0.5 * (
      1 + cos(pi * 2 * num_periods * step / decay_steps))
  decayed = (alpha + linear_decay + eps_t) * cosine_decay + beta
  return initial_learning_rate * decayed

where eps_t is 0-centered gaussian noise with variance initial_variance / (1 + global_step) ** variance_decay

Example usage:

decay_steps = 1000
lr_decayed_fn = (
  tf.keras.experimental.NoisyLinearCosineDecay(
    initial_learning_rate, decay_steps))

You can pass this schedule directly into a tf.keras.optimizers.Optimizer as the learning rate. The learning rate schedule is also serializable and deserializable using tf.keras.optimizers.schedules.serialize and tf.keras.optimizers.schedules.deserialize.

Args:

initial_learning_rate: A scalar float32 or float64 Tensor or a Python number. The initial learning rate.
decay_steps: A scalar int32 or int64 Tensor or a Python number. Number of steps to decay over.
initial_variance: initial variance for the noise. See computation above.
variance_decay: decay for the noise's variance. See computation above.
num_periods: Number of periods in the cosine part of the decay. See computation above.
alpha: See computation above.
beta: See computation above.
name: String. Optional name of the operation. Defaults to 'NoisyLinearCosineDecay'.

Returns:

A 1-arg callable learning rate schedule that takes the current optimizer step and outputs the decayed learning rate, a scalar Tensor of the same type as initial_learning_rate.

Methods