► Keras 2 API 文档 / 损失函数 / 概率损失

概率损失

`BinaryCrossentropy` class

tf_keras.losses.BinaryCrossentropy(
    from_logits=False,
    label_smoothing=0.0,
    axis=-1,
    reduction="auto",
    name="binary_crossentropy",
)

Computes the cross-entropy loss between true labels and predicted labels.

Use this cross-entropy loss for binary (0 or 1) classification applications. The loss function requires the following inputs:

y_true (true label): This is either 0 or 1.
y_pred (predicted value): This is the model's prediction, i.e, a single floating-point value which either represents a logit, (i.e, value in [-inf, inf] when from_logits=True) or a probability (i.e, value in [0., 1.] when from_logits=False).

Recommended Usage: (set from_logits=True)

With tf.keras API:

model.compile(
    loss=tf.keras.losses.BinaryCrossentropy(from_logits=True),
    ....
)

As a standalone function:

>>> # Example 1: (batch_size = 1, number of samples = 4)
>>> y_true = [0, 1, 0, 0]
>>> y_pred = [-18.6, 0.51, 2.94, -12.8]
>>> bce = tf.keras.losses.BinaryCrossentropy(from_logits=True)
>>> bce(y_true, y_pred).numpy()
0.865

>>> # Example 2: (batch_size = 2, number of samples = 4)
>>> y_true = [[0, 1], [0, 0]]
>>> y_pred = [[-18.6, 0.51], [2.94, -12.8]]
>>> # Using default 'auto'/'sum_over_batch_size' reduction type.
>>> bce = tf.keras.losses.BinaryCrossentropy(from_logits=True)
>>> bce(y_true, y_pred).numpy()
0.865
>>> # Using 'sample_weight' attribute
>>> bce(y_true, y_pred, sample_weight=[0.8, 0.2]).numpy()
0.243
>>> # Using 'sum' reduction` type.
>>> bce = tf.keras.losses.BinaryCrossentropy(from_logits=True,
...     reduction=tf.keras.losses.Reduction.SUM)
>>> bce(y_true, y_pred).numpy()
1.730
>>> # Using 'none' reduction type.
>>> bce = tf.keras.losses.BinaryCrossentropy(from_logits=True,
...     reduction=tf.keras.losses.Reduction.NONE)
>>> bce(y_true, y_pred).numpy()
array([0.235, 1.496], dtype=float32)

Default Usage: (set from_logits=False)

>>> # Make the following updates to the above "Recommended Usage" section
>>> # 1. Set `from_logits=False`
>>> tf.keras.losses.BinaryCrossentropy() # OR ...('from_logits=False')
>>> # 2. Update `y_pred` to use probabilities instead of logits
>>> y_pred = [0.6, 0.3, 0.2, 0.8] # OR [[0.6, 0.3], [0.2, 0.8]]

[source]

`CategoricalCrossentropy` class

tf_keras.losses.CategoricalCrossentropy(
    from_logits=False,
    label_smoothing=0.0,
    axis=-1,
    reduction="auto",
    name="categorical_crossentropy",
)

Computes the crossentropy loss between the labels and predictions.

Use this crossentropy loss function when there are two or more label classes. We expect labels to be provided in a one_hot representation. If you want to provide labels as integers, please use SparseCategoricalCrossentropy loss. There should be # classes floating point values per feature.

In the snippet below, there is # classes floating pointing values per example. The shape of both y_pred and y_true are [batch_size, num_classes].

Standalone usage:

>>> y_true = [[0, 1, 0], [0, 0, 1]]
>>> y_pred = [[0.05, 0.95, 0], [0.1, 0.8, 0.1]]
>>> # Using 'auto'/'sum_over_batch_size' reduction type.
>>> cce = tf.keras.losses.CategoricalCrossentropy()
>>> cce(y_true, y_pred).numpy()
1.177

>>> # Calling with 'sample_weight'.
>>> cce(y_true, y_pred, sample_weight=tf.constant([0.3, 0.7])).numpy()
0.814

>>> # Using 'sum' reduction type.
>>> cce = tf.keras.losses.CategoricalCrossentropy(
...     reduction=tf.keras.losses.Reduction.SUM)
>>> cce(y_true, y_pred).numpy()
2.354

>>> # Using 'none' reduction type.
>>> cce = tf.keras.losses.CategoricalCrossentropy(
...     reduction=tf.keras.losses.Reduction.NONE)
>>> cce(y_true, y_pred).numpy()
array([0.0513, 2.303], dtype=float32)

Usage with the compile() API:

model.compile(optimizer='sgd',
              loss=tf.keras.losses.CategoricalCrossentropy())

[source]

`SparseCategoricalCrossentropy` class

tf_keras.losses.SparseCategoricalCrossentropy(
    from_logits=False,
    ignore_class=None,
    reduction="auto",
    name="sparse_categorical_crossentropy",
)

Computes the crossentropy loss between the labels and predictions.

Use this crossentropy loss function when there are two or more label classes. We expect labels to be provided as integers. If you want to provide labels using one-hot representation, please use CategoricalCrossentropy loss. There should be # classes floating point values per feature for y_pred and a single floating point value per feature for y_true.

In the snippet below, there is a single floating point value per example for y_true and # classes floating pointing values per example for y_pred. The shape of y_true is [batch_size] and the shape of y_pred is [batch_size, num_classes].

Standalone usage:

>>> y_true = [1, 2]
>>> y_pred = [[0.05, 0.95, 0], [0.1, 0.8, 0.1]]
>>> # Using 'auto'/'sum_over_batch_size' reduction type.
>>> scce = tf.keras.losses.SparseCategoricalCrossentropy()
>>> scce(y_true, y_pred).numpy()
1.177

>>> # Calling with 'sample_weight'.
>>> scce(y_true, y_pred, sample_weight=tf.constant([0.3, 0.7])).numpy()
0.814

>>> # Using 'sum' reduction type.
>>> scce = tf.keras.losses.SparseCategoricalCrossentropy(
...     reduction=tf.keras.losses.Reduction.SUM)
>>> scce(y_true, y_pred).numpy()
2.354

>>> # Using 'none' reduction type.
>>> scce = tf.keras.losses.SparseCategoricalCrossentropy(
...     reduction=tf.keras.losses.Reduction.NONE)
>>> scce(y_true, y_pred).numpy()
array([0.0513, 2.303], dtype=float32)

Usage with the compile() API:

model.compile(optimizer='sgd',
              loss=tf.keras.losses.SparseCategoricalCrossentropy())

[source]

`Poisson` class

tf_keras.losses.Poisson(reduction="auto", name="poisson")

Computes the Poisson loss between y_true & y_pred.

loss = y_pred - y_true * log(y_pred)

Standalone usage:

>>> y_true = [[0., 1.], [0., 0.]]
>>> y_pred = [[1., 1.], [0., 0.]]
>>> # Using 'auto'/'sum_over_batch_size' reduction type.
>>> p = tf.keras.losses.Poisson()
>>> p(y_true, y_pred).numpy()
0.5

>>> # Calling with 'sample_weight'.
>>> p(y_true, y_pred, sample_weight=[0.8, 0.2]).numpy()
0.4

>>> # Using 'sum' reduction type.
>>> p = tf.keras.losses.Poisson(
...     reduction=tf.keras.losses.Reduction.SUM)
>>> p(y_true, y_pred).numpy()
0.999

>>> # Using 'none' reduction type.
>>> p = tf.keras.losses.Poisson(
...     reduction=tf.keras.losses.Reduction.NONE)
>>> p(y_true, y_pred).numpy()
array([0.999, 0.], dtype=float32)

Usage with the compile() API:

model.compile(optimizer='sgd', loss=tf.keras.losses.Poisson())

[source]

`binary_crossentropy` function

tf_keras.losses.binary_crossentropy(
    y_true, y_pred, from_logits=False, label_smoothing=0.0, axis=-1
)

Computes the binary crossentropy loss.

Standalone usage:

>>> y_true = [[0, 1], [0, 0]]
>>> y_pred = [[0.6, 0.4], [0.4, 0.6]]
>>> loss = tf.keras.losses.binary_crossentropy(y_true, y_pred)
>>> assert loss.shape == (2,)
>>> loss.numpy()
array([0.916 , 0.714], dtype=float32)

Arguments

y_true: Ground truth values. shape = [batch_size, d0, .. dN].
y_pred: The predicted values. shape = [batch_size, d0, .. dN].
from_logits: Whether y_pred is expected to be a logits tensor. By default, we assume that y_pred encodes a probability distribution.
label_smoothing: Float in [0, 1]. If > 0 then smooth the labels by squeezing them towards 0.5 That is, using 1. - 0.5 * label_smoothing for the target class and 0.5 * label_smoothing for the non-target class.
axis: The axis along which the mean is computed. Defaults to -1.

Returns

Binary crossentropy loss value. shape = [batch_size, d0, .. dN-1].

[source]

`categorical_crossentropy` function

tf_keras.losses.categorical_crossentropy(
    y_true, y_pred, from_logits=False, label_smoothing=0.0, axis=-1
)

Computes the categorical crossentropy loss.

Standalone usage:

>>> y_true = [[0, 1, 0], [0, 0, 1]]
>>> y_pred = [[0.05, 0.95, 0], [0.1, 0.8, 0.1]]
>>> loss = tf.keras.losses.categorical_crossentropy(y_true, y_pred)
>>> assert loss.shape == (2,)
>>> loss.numpy()
array([0.0513, 2.303], dtype=float32)

Arguments

y_true: Tensor of one-hot true targets.
y_pred: Tensor of predicted targets.
from_logits: Whether y_pred is expected to be a logits tensor. By default, we assume that y_pred encodes a probability distribution.
label_smoothing: Float in [0, 1]. If > 0 then smooth the labels. For example, if 0.1, use 0.1 / num_classes for non-target labels and 0.9 + 0.1 / num_classes for target labels.
axis: Defaults to -1. The dimension along which the entropy is computed.

Returns

Categorical crossentropy loss value.

[source]

`sparse_categorical_crossentropy` function

tf_keras.losses.sparse_categorical_crossentropy(
    y_true, y_pred, from_logits=False, axis=-1, ignore_class=None
)

Computes the sparse categorical crossentropy loss.

Standalone usage:

>>> y_true = [1, 2]
>>> y_pred = [[0.05, 0.95, 0], [0.1, 0.8, 0.1]]
>>> loss = tf.keras.losses.sparse_categorical_crossentropy(y_true, y_pred)
>>> assert loss.shape == (2,)
>>> loss.numpy()
array([0.0513, 2.303], dtype=float32)

>>> y_true = [[[ 0,  2],
...            [-1, -1]],
...           [[ 0,  2],
...            [-1, -1]]]
>>> y_pred = [[[[1.0, 0.0, 0.0], [0.0, 0.0, 1.0]],
...             [[0.2, 0.5, 0.3], [0.0, 1.0, 0.0]]],
...           [[[1.0, 0.0, 0.0], [0.0, 0.5, 0.5]],
...            [[0.2, 0.5, 0.3], [0.0, 1.0, 0.0]]]]
>>> loss = tf.keras.losses.sparse_categorical_crossentropy(
...   y_true, y_pred, ignore_class=-1)
>>> loss.numpy()
array([[[2.3841855e-07, 2.3841855e-07],
        [0.0000000e+00, 0.0000000e+00]],
       [[2.3841855e-07, 6.9314730e-01],
        [0.0000000e+00, 0.0000000e+00]]], dtype=float32)

Arguments

y_true: Ground truth values.
y_pred: The predicted values.
from_logits: Whether y_pred is expected to be a logits tensor. By default, we assume that y_pred encodes a probability distribution.
axis: Defaults to -1. The dimension along which the entropy is computed.
ignore_class: Optional integer. The ID of a class to be ignored during loss computation. This is useful, for example, in segmentation problems featuring a "void" class (commonly -1 or 255) in segmentation maps. By default (ignore_class=None), all classes are considered.

Returns

Sparse categorical crossentropy loss value.

[source]

`poisson` function

tf_keras.losses.poisson(y_true, y_pred)

Computes the Poisson loss between y_true and y_pred.

The Poisson loss is the mean of the elements of the Tensor y_pred - y_true * log(y_pred).

Standalone usage:

>>> y_true = np.random.randint(0, 2, size=(2, 3))
>>> y_pred = np.random.random(size=(2, 3))
>>> loss = tf.keras.losses.poisson(y_true, y_pred)
>>> assert loss.shape == (2,)
>>> y_pred = y_pred + 1e-7
>>> assert np.allclose(
...     loss.numpy(), np.mean(y_pred - y_true * np.log(y_pred), axis=-1),
...     atol=1e-5)

Arguments

y_true: Ground truth values. shape = [batch_size, d0, .. dN].
y_pred: The predicted values. shape = [batch_size, d0, .. dN].

Returns

Poisson loss value. shape = [batch_size, d0, .. dN-1].

Raises

InvalidArgumentError: If y_true and y_pred have incompatible shapes.

[source]

`KLDivergence` class

tf_keras.losses.KLDivergence(reduction="auto", name="kl_divergence")

Computes Kullback-Leibler divergence loss between y_true & y_pred.

loss = y_true * log(y_true / y_pred)

See: https://en.wikipedia.org/wiki/Kullback%E2%80%93Leibler_divergence

Standalone usage:

>>> y_true = [[0, 1], [0, 0]]
>>> y_pred = [[0.6, 0.4], [0.4, 0.6]]
>>> # Using 'auto'/'sum_over_batch_size' reduction type.
>>> kl = tf.keras.losses.KLDivergence()
>>> kl(y_true, y_pred).numpy()
0.458

>>> # Calling with 'sample_weight'.
>>> kl(y_true, y_pred, sample_weight=[0.8, 0.2]).numpy()
0.366

>>> # Using 'sum' reduction type.
>>> kl = tf.keras.losses.KLDivergence(
...     reduction=tf.keras.losses.Reduction.SUM)
>>> kl(y_true, y_pred).numpy()
0.916

>>> # Using 'none' reduction type.
>>> kl = tf.keras.losses.KLDivergence(
...     reduction=tf.keras.losses.Reduction.NONE)
>>> kl(y_true, y_pred).numpy()
array([0.916, -3.08e-06], dtype=float32)

Usage with the compile() API:

model.compile(optimizer='sgd', loss=tf.keras.losses.KLDivergence())

[source]

`kl_divergence` function

tf_keras.losses.kl_divergence(y_true, y_pred)

Computes Kullback-Leibler divergence loss between y_true & y_pred.

loss = y_true * log(y_true / y_pred)

See: https://en.wikipedia.org/wiki/Kullback%E2%80%93Leibler_divergence

Standalone usage:

>>> y_true = np.random.randint(0, 2, size=(2, 3)).astype(np.float64)
>>> y_pred = np.random.random(size=(2, 3))
>>> loss = tf.keras.losses.kullback_leibler_divergence(y_true, y_pred)
>>> assert loss.shape == (2,)
>>> y_true = tf.keras.backend.clip(y_true, 1e-7, 1)
>>> y_pred = tf.keras.backend.clip(y_pred, 1e-7, 1)
>>> assert np.array_equal(
...     loss.numpy(), np.sum(y_true * np.log(y_true / y_pred), axis=-1))

Arguments

y_true: Tensor of true targets.
y_pred: Tensor of predicted targets.

Returns

A Tensor with loss.

Raises

TypeError: If y_true cannot be cast to the y_pred.dtype.

概率损失

BinaryCrossentropy class

CategoricalCrossentropy class

SparseCategoricalCrossentropy class

Poisson class

binary_crossentropy function

categorical_crossentropy function

sparse_categorical_crossentropy function

poisson function

KLDivergence class

kl_divergence function

概率损失

BinaryCrossentropy class

CategoricalCrossentropy class

SparseCategoricalCrossentropy class

Poisson class

binary_crossentropy function

categorical_crossentropy function

sparse_categorical_crossentropy function

poisson function

KLDivergence class

kl_divergence function

`BinaryCrossentropy` class

`CategoricalCrossentropy` class

`SparseCategoricalCrossentropy` class

`Poisson` class

`binary_crossentropy` function

`categorical_crossentropy` function

`sparse_categorical_crossentropy` function

`poisson` function

`KLDivergence` class

`kl_divergence` function