规范化层

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Normalization class

tf_keras.layers.Normalization(
    axis=-1, mean=None, variance=None, invert=False, **kwargs
)

A preprocessing layer which normalizes continuous features.

This layer will shift and scale inputs into a distribution centered around 0 with standard deviation 1. It accomplishes this by precomputing the mean and variance of the data, and calling (input - mean) / sqrt(var) at runtime.

The mean and variance values for the layer must be either supplied on construction or learned via adapt(). adapt() will compute the mean and variance of the data and store them as the layer's weights. adapt() should be called before fit(), evaluate(), or predict().

For an overview and full list of preprocessing layers, see the preprocessing guide.

Arguments

• axis: Integer, tuple of integers, or None. The axis or axes that should have a separate mean and variance for each index in the shape. For example, if shape is (None, 5) and axis=1, the layer will track 5 separate mean and variance values for the last axis. If axis is set to None, the layer will normalize all elements in the input by a scalar mean and variance. When -1 the last axis of the input is assumed to be a feature dimension and is normalized per index. Note that in the specific case of batched scalar inputs where the only axis is the batch axis, the default will normalize each index in the batch separately. In this case, consider passing axis=None. Defaults to -1.
• mean: The mean value(s) to use during normalization. The passed value(s) will be broadcast to the shape of the kept axes above; if the value(s) cannot be broadcast, an error will be raised when this layer's build() method is called.
• variance: The variance value(s) to use during normalization. The passed value(s) will be broadcast to the shape of the kept axes above; if the value(s) cannot be broadcast, an error will be raised when this layer's build() method is called.
• invert: If True, this layer will apply the inverse transformation to its inputs: it would turn a normalized input back into its original form.

Examples

Calculate a global mean and variance by analyzing the dataset in adapt().

>>> adapt_data = np.array([1., 2., 3., 4., 5.], dtype='float32')
>>> input_data = np.array([1., 2., 3.], dtype='float32')
>>> layer = tf.keras.layers.Normalization(axis=None)
>>> layer.adapt(adapt_data)
>>> layer(input_data)
<tf.Tensor: shape=(3,), dtype=float32, numpy=
array([-1.4142135, -0.70710677, 0.], dtype=float32)>

Calculate a mean and variance for each index on the last axis.

>>> adapt_data = np.array([[0., 7., 4.],
...                        [2., 9., 6.],
...                        [0., 7., 4.],
...                        [2., 9., 6.]], dtype='float32')
>>> input_data = np.array([[0., 7., 4.]], dtype='float32')
>>> layer = tf.keras.layers.Normalization(axis=-1)
>>> layer.adapt(adapt_data)
>>> layer(input_data)
<tf.Tensor: shape=(1, 3), dtype=float32, numpy=
array([-1., -1., -1.], dtype=float32)>

Pass the mean and variance directly.

>>> input_data = np.array([[1.], [2.], [3.]], dtype='float32')
>>> layer = tf.keras.layers.Normalization(mean=3., variance=2.)
>>> layer(input_data)
<tf.Tensor: shape=(3, 1), dtype=float32, numpy=
array([[-1.4142135 ],
       [-0.70710677],
       [ 0.        ]], dtype=float32)>

Use the layer to de-normalize inputs (after adapting the layer).

>>> adapt_data = np.array([[0., 7., 4.],
...                        [2., 9., 6.],
...                        [0., 7., 4.],
...                        [2., 9., 6.]], dtype='float32')
>>> input_data = np.array([[1., 2., 3.]], dtype='float32')
>>> layer = tf.keras.layers.Normalization(axis=-1, invert=True)
>>> layer.adapt(adapt_data)
>>> layer(input_data)
<tf.Tensor: shape=(1, 3), dtype=float32, numpy=
array([2., 10., 8.], dtype=float32)>