Learning rate scheduler.
callback_learning_rate_scheduler(schedule)a function that takes an epoch index as input (integer, indexed from 0) and current learning rate and returns a new learning rate as output (float).
Other callbacks:
callback_csv_logger(),
callback_early_stopping(),
callback_lambda(),
callback_model_checkpoint(),
callback_progbar_logger(),
callback_reduce_lr_on_plateau(),
callback_remote_monitor(),
callback_tensorboard(),
callback_terminate_on_naan()