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This class allows to extend optimizers with the lookahead mechanism.

The mechanism is proposed by Michael R. Zhang in the paper Lookahead Optimizer: k steps forward, 1 step back. The optimizer iteratively updates two sets of weights: the search directions for weights are chosen by the inner optimizer, while the "slow weights" are updated each k steps based on the directions of the "fast weights" and the two sets of weights are synchronized. This method improves the learning stability and lowers the variance of its inner optimizer.

Example of usage:

opt = tf.keras.optimizers.SGD(learning_rate)
opt = tfa.optimizers.Lookahead(opt)


  • optimizer: The original optimizer that will be used to compute and apply the gradients.
  • sync_period: An integer. The synchronization period of lookahead. Enable lookahead mechanism by setting it with a positive value.
  • slow_step_size: A floating point value. The ratio for updating the slow weights.
  • name: Optional name for the operations created when applying gradients. Defaults to "Lookahead".
  • **kwargs: keyword arguments. Allowed to be {clipnorm, clipvalue, lr, decay}. clipnorm is clip gradients by norm; clipvalue is clip gradients by value, decay is included for backward compatibility to allow time inverse decay of learning rate. lr is included for backward compatibility, recommended to use learning_rate instead.


  • iterations: Variable. The number of training steps this Optimizer has run.
  • learning_rate
  • lr
  • weights: Returns variables of this Optimizer based on the order created.



Add a new slot variable for var.



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Apply gradients to variables.

This is the second part of minimize(). It returns an Operation that applies gradients.


  • grads_and_vars: List of (gradient, variable) pairs.
  • name: Optional name for the returned operation. Default to the name passed to the Optimizer constructor.


An Operation that applies the specified gradients. The iterations will be automatically increased by 1.


  • TypeError: If grads_and_vars is malformed.
  • ValueError: If none of the variables have gradients.


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Creates an optimizer from its config.

This method is the reverse of get_config, capable of instantiating the same optimizer from the config dictionary.


  • config: A Python dictionary, typically the output of get_config.
  • custom_objects: A Python dictionary mapping names to additional Python objects used to create this optimizer, such as a function used for a hyperparameter.


An optimizer instance.


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Returns the config of the optimimizer.

An optimizer config is a Python dictionary (serializable) containing the configuration of an optimizer. The same optimizer can be reinstantiated later (without any saved state) from this configuration.


Python dictionary.


Returns gradients of loss with respect to params.


  • loss: Loss tensor.
  • params: List of variables.


List of gradient tensors.


  • ValueError: In case any gradient cannot be computed (e.g. if gradient function not implemented).



A list of names for this optimizer's slots.




Minimize loss by updating var_list.

This method simply computes gradient using tf.GradientTape and calls apply_gradients(). If you want to process the gradient before applying then call tf.GradientTape and apply_gradients() explicitly instead of using this function.


  • loss: A callable taking no arguments which returns the value to minimize.
  • var_list: list or tuple of Variable objects to update to minimize loss, or a callable returning the list or tuple of Variable objects. Use callable when the variable list would otherwise be incomplete before minimize since the variables are created at the first time loss is called.
  • grad_loss: Optional. A Tensor holding the gradient computed for loss.
  • name: Optional name for the returned operation.


An Operation that updates the variables in var_list. The iterations will be automatically increased by 1.


  • ValueError: If some of the variables are not Variable objects.



Returns variables of this Optimizer based on the order created.