tf.keras.losses.Loss

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Class Loss

Loss base class.

Aliases:

• Class tf.compat.v1.keras.losses.Loss
• Class tf.compat.v2.keras.losses.Loss
• Class tf.compat.v2.losses.Loss

To be implemented by subclasses: * call(): Contains the logic for loss calculation using y_true, y_pred.

Example subclass implementation:

class MeanSquaredError(Loss):
  def call(self, y_true, y_pred):
    y_pred = ops.convert_to_tensor(y_pred)
    y_true = math_ops.cast(y_true, y_pred.dtype)
    return K.mean(math_ops.square(y_pred - y_true), axis=-1)

When used with tf.distribute.Strategy, outside of built-in training loops such as tf.keras compile and fit, please use 'SUM' or 'NONE' reduction types, and reduce losses explicitly in your training loop. Using 'AUTO' or 'SUM_OVER_BATCH_SIZE' will raise an error.

Please see https://www.tensorflow.org/alpha/tutorials/distribute/training_loops for more details on this.

You can implement 'SUM_OVER_BATCH_SIZE' using global batch size like:

with strategy.scope():
  loss_obj = tf.keras.losses.CategoricalCrossentropy(
      reduction=tf.keras.losses.Reduction.NONE)
  ....
  loss = (tf.reduce_sum(loss_obj(labels, predictions)) *
          (1. / global_batch_size))

Args:

• reduction: (Optional) Type of tf.keras.losses.Reduction to apply to loss. Default value is AUTO. AUTO indicates that the reduction option will be determined by the usage context. For almost all cases this defaults to SUM_OVER_BATCH_SIZE. When used with tf.distribute.Strategy, outside of built-in training loops such as tf.keras compile and fit, using AUTO or SUM_OVER_BATCH_SIZE will raise an error. Please see https://www.tensorflow.org/alpha/tutorials/distribute/training_loops for more details on this.
• name: Optional name for the op.

__init__

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__init__(
    reduction=losses_utils.ReductionV2.AUTO,
    name=None
)

Initialize self. See help(type(self)) for accurate signature.

Methods

tf.keras.losses.Loss.__call__

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__call__(
    y_true,
    y_pred,
    sample_weight=None
)

Invokes the Loss instance.

Args:

• y_true: Ground truth values. shape = [batch_size, d0, .. dN]
• y_pred: The predicted values. shape = [batch_size, d0, .. dN]
• sample_weight: Optional sample_weight acts as a coefficient for the loss. If a scalar is provided, then the loss is simply scaled by the given value. If sample_weight is a tensor of size [batch_size], then the total loss for each sample of the batch is rescaled by the corresponding element in the sample_weight vector. If the shape of sample_weight is [batch_size, d0, .. dN-1] (or can be broadcasted to this shape), then each loss element of y_pred is scaled by the corresponding value of sample_weight. (Note ondN-1: all loss functions reduce by 1 dimension, usually axis=-1.)

Returns:

Weighted loss float Tensor. If reduction is NONE, this has shape [batch_size, d0, .. dN-1]; otherwise, it is scalar. (Note dN-1 because all loss functions reduce by 1 dimension, usually axis=-1.)

Raises:

• ValueError: If the shape of sample_weight is invalid.

tf.keras.losses.Loss.call

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call(
    y_true,
    y_pred
)

Invokes the Loss instance.

Args:

• y_true: Ground truth values, with the same shape as 'y_pred'.
• y_pred: The predicted values.

tf.keras.losses.Loss.from_config

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@classmethod
from_config(
    cls,
    config
)

Instantiates a Loss from its config (output of get_config()).

Args:

• config: Output of get_config().

Returns:

A Loss instance.

tf.keras.losses.Loss.get_config

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get_config()