# A `LearningRateSchedule`

that uses a cosine decay schedule with restarts.

Source: `R/optimizers-schedules.R`

`learning_rate_schedule_cosine_decay_restarts.Rd`

See Loshchilov & Hutter, ICLR2016, SGDR: Stochastic Gradient Descent with Warm Restarts.

When training a model, it is often useful to lower the learning rate as
the training progresses. This schedule applies a cosine decay function with
restarts 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 backend variable that you increment at each training step.

The schedule is 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.

The learning rate multiplier first decays
from 1 to `alpha`

for `first_decay_steps`

steps. Then, a warm
restart is performed. Each new warm restart runs for `t_mul`

times more
steps and with `m_mul`

times initial learning rate as the new learning rate.

Example usage:

```
first_decay_steps <- 1000
lr_decayed_fn <- learning_rate_schedule_cosine_decay_restarts(
0.001,
first_decay_steps)
```

You can pass this schedule directly into a `optimizer`

as the learning rate. The learning rate schedule is also serializable and
deserializable using `keras$optimizers$schedules$serialize`

and
`keras$optimizers$schedules$deserialize`

.

## Usage

```
learning_rate_schedule_cosine_decay_restarts(
initial_learning_rate,
first_decay_steps,
t_mul = 2,
m_mul = 1,
alpha = 0,
name = "SGDRDecay"
)
```

## Arguments

- initial_learning_rate
A float. The initial learning rate.

- first_decay_steps
An integer. Number of steps to decay over.

- t_mul
A float. Used to derive the number of iterations in the i-th period.

- m_mul
A float. Used to derive the initial learning rate of the i-th period.

- alpha
A float. Minimum learning rate value as a fraction of the

`initial_learning_rate`

.- name
String. Optional name of the operation. Defaults to

`"SGDRDecay"`

.

## Value

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`

.

## See also

Other optimizer learning rate schedules: `LearningRateSchedule()`

`learning_rate_schedule_cosine_decay()`

`learning_rate_schedule_exponential_decay()`

`learning_rate_schedule_inverse_time_decay()`

`learning_rate_schedule_piecewise_constant_decay()`

`learning_rate_schedule_polynomial_decay()`