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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
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#     http://www.apache.org/licenses/LICENSE-2.0
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# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
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# ==============================================================================

import tensorflow as tf

from tensorflow_addons.utils import types


@tf.keras.utils.register_keras_serializable(package="Addons")
def snake(logits: types.TensorLike, frequency: types.Number = 1) -> tf.Tensor:
    """Snake activation to learn periodic functions.

    https://arxiv.org/abs/2006.08195

    Args:
        logits: Input tensor.
        frequency: A scalar, frequency of the periodic part.
    Returns:
        Tensor of the same type and shape as `logits`.
    """

    logits = tf.convert_to_tensor(logits)
    frequency = tf.cast(frequency, logits.dtype)

    return logits + (1 - tf.cos(2 * frequency * logits)) / (2 * frequency)
