# Higher level ops for building neural network layers.

This package provides several ops that take care of creating variables that are used internally in a consistent way and provide the building blocks for many common machine learning algorithms.

### tf.contrib.layers.avg_pool2d(*args, **kwargs)

Adds a 2D average pooling op.

It is assumed that the pooling is done per image but not in batch or channels.

##### Args:
• inputs: A Tensor of size [batch_size, height, width, channels].
• kernel_size: A list of length 2: [kernel_height, kernel_width] of the pooling kernel over which the op is computed. Can be an int if both values are the same.
• stride: A list of length 2: [stride_height, stride_width]. Can be an int if both strides are the same. Note that presently both strides must have the same value.
• padding: The padding method, either 'VALID' or 'SAME'.
• outputs_collections: The collections to which the outputs are added.
• scope: Optional scope for name_scope.
##### Returns:

A Tensor representing the results of the pooling operation.

### tf.contrib.layers.batch_norm(*args, **kwargs)

Adds a Batch Normalization layer from http://arxiv.org/abs/1502.03167.

"Batch Normalization: Accelerating Deep Network Training by Reducing Internal Covariate Shift"

Sergey Ioffe, Christian Szegedy

Can be used as a normalizer function for conv2d and fully_connected.

update_ops = tf.get_collection(tf.GraphKeys.UPDATE_OPS) if update_ops: updates = tf.group(*update_ops) total_loss = control_flow_ops.with_dependencies([updates], total_loss)

One can set update_collections=None to force the updates in place, but that can have speed penalty, specially in distributed settings.

##### Args:
• inputs: a tensor with 2 or more dimensions, where the first dimension has batch_size. The normalization is over all but the last dimension.
• decay: decay for the moving average.
• center: If True, subtract beta. If False, beta is ignored.
• scale: If True, multiply by gamma. If False, gamma is not used. When the next layer is linear (also e.g. nn.relu), this can be disabled since the scaling can be done by the next layer.
• epsilon: small float added to variance to avoid dividing by zero.
• activation_fn: activation function, default set to None to skip it and maintain a linear activation.
• updates_collections: collections to collect the update ops for computation. The updates_ops need to be excuted with the train_op. If None, a control dependency would be added to make sure the updates are computed in place.
• is_training: whether or not the layer is in training mode. In training mode it would accumulate the statistics of the moments into moving_mean and moving_variance using an exponential moving average with the given decay. When it is not in training mode then it would use the values of the moving_mean and the moving_variance.
• reuse: whether or not the layer and its variables should be reused. To be able to reuse the layer scope must be given.
• variables_collections: optional collections for the variables.
• outputs_collections: collections to add the outputs.
• trainable: If True also add variables to the graph collection GraphKeys.TRAINABLE_VARIABLES (see tf.Variable).
• scope: Optional scope for variable_scope.
##### Returns:

A Tensor representing the output of the operation.

##### Raises:
• ValueError: if rank or last dimension of inputs is undefined.

### tf.contrib.layers.convolution2d(*args, **kwargs)

Adds a 2D convolution followed by an optional batch_norm layer.

convolution2d creates a variable called weights, representing the convolutional kernel, that is convolved with the inputs to produce a Tensor of activations. If a normalizer_fn is provided (such as batch_norm), it is then applied. Otherwise, if normalizer_fn is None and a biases_initializer is provided then a biases variable would be created and added the activations. Finally, if activation_fn is not None, it is applied to the activations as well.

Performs a'trous convolution with input stride equal to rate if rate is greater than one.

##### Args:
• inputs: a 4-D tensor [batch_size, height, width, channels].
• num_outputs: integer, the number of output filters.
• kernel_size: a list of length 2 [kernel_height, kernel_width] of of the filters. Can be an int if both values are the same.
• stride: a list of length 2 [stride_height, stride_width]. Can be an int if both strides are the same. Note that presently both strides must have the same value.
• padding: one of VALID or SAME.
• rate: integer. If less than or equal to 1, a standard convolution is used. If greater than 1, than the a'trous convolution is applied and stride must be set to 1.
• activation_fn: activation function, set to None to skip it and maintain a linear activation.
• normalizer_fn: normalization function to use instead of biases. If normalizer_fn is provided then biases_initializer and biases_regularizer are ignored and biases are not created nor added. default set to None for no normalizer function
• normalizer_params: normalization function parameters.
• weights_initializer: An initializer for the weights.
• weights_regularizer: Optional regularizer for the weights.
• biases_initializer: An initializer for the biases. If None skip biases.
• biases_regularizer: Optional regularizer for the biases.
• reuse: whether or not the layer and its variables should be reused. To be able to reuse the layer scope must be given.
• variables_collections: optional list of collections for all the variables or a dictionay containing a different list of collection per variable.
• outputs_collections: collection to add the outputs.
• trainable: If True also add variables to the graph collection GraphKeys.TRAINABLE_VARIABLES (see tf.Variable).
• scope: Optional scope for variable_scope.
##### Returns:

a tensor representing the output of the operation.

##### Raises:
• ValueError: if both 'rate' and stride are larger than one.

### tf.contrib.layers.convolution2d_in_plane(*args, **kwargs)

Performs the same in-plane convolution to each channel independently.

This is useful for performing various simple channel-independent convolution operations such as image gradients:

image = tf.constant(..., shape=(16, 240, 320, 3)) vert_gradients = layers.conv2d_in_plane(image, kernel=[1, -1], kernel_size=[2, 1]) horz_gradients = layers.conv2d_in_plane(image, kernel=[1, -1], kernel_size=[1, 2])

##### Args:
• inputs: a 4-D tensor with dimensions [batch_size, height, width, channels].
• kernel_size: a list of length 2 holding the [kernel_height, kernel_width] of of the pooling. Can be an int if both values are the same.
• stride: a list of length 2 [stride_height, stride_width]. Can be an int if both strides are the same. Note that presently both strides must have the same value.
• padding: the padding type to use, either 'SAME' or 'VALID'.
• activation_fn: activation function, set to None to skip it and maintain a linear activation.
• normalizer_fn: normalization function to use instead of biases. If normalizer_fn is provided then biases_initializer and biases_regularizer are ignored and biases are not created nor added. default set to None for no normalizer function
• normalizer_params: normalization function parameters.
• weights_initializer: An initializer for the weights.
• weights_regularizer: Optional regularizer for the weights.
• biases_initializer: An initializer for the biases. If None skip biases.
• biases_regularizer: Optional regularizer for the biases.
• reuse: whether or not the layer and its variables should be reused. To be able to reuse the layer scope must be given.
• variables_collections: optional list of collections for all the variables or a dictionay containing a different list of collection per variable.
• outputs_collections: collection to add the outputs.
• trainable: If True also add variables to the graph collection GraphKeys.TRAINABLE_VARIABLES (see tf.Variable).
• scope: Optional scope for variable_scope.
##### Returns:

A Tensor representing the output of the operation.

### tf.contrib.layers.convolution2d_transpose(*args, **kwargs)

Adds a convolution2d_transpose with an optional batch normalization layer.

The function creates a variable called weights, representing the kernel, that is convolved with the input. If batch_norm_params is None, a second variable called 'biases' is added to the result of the operation.

##### Args:
• inputs: a tensor of size [batch_size, height, width, channels].
• num_outputs: integer, the number of output filters.
• kernel_size: a list of length 2 holding the [kernel_height, kernel_width] of of the filters. Can be an int if both values are the same.
• stride: a list of length 2: [stride_height, stride_width]. Can be an int if both strides are the same. Note that presently both strides must have the same value.
• padding: one of 'VALID' or 'SAME'.
• activation_fn: activation function, set to None to skip it and maintain a linear activation.
• normalizer_fn: normalization function to use instead of biases. If normalizer_fn is provided then biases_initializer and biases_regularizer are ignored and biases are not created nor added. default set to None for no normalizer function
• normalizer_params: normalization function parameters.
• weights_initializer: An initializer for the weights.
• weights_regularizer: Optional regularizer for the weights.
• biases_initializer: An initializer for the biases. If None skip biases.
• biases_regularizer: Optional regularizer for the biases.
• reuse: whether or not the layer and its variables should be reused. To be able to reuse the layer scope must be given.
• variables_collections: optional list of collections for all the variables or a dictionay containing a different list of collection per variable.
• outputs_collections: collection to add the outputs.
• trainable: whether or not the variables should be trainable or not.
• scope: Optional scope for variable_scope.
##### Returns:

a tensor representing the output of the operation.

##### Raises:
• ValueError: if 'kernel_size' is not a list of length 2.

### tf.contrib.layers.flatten(*args, **kwargs)

Flattens the input while maintaining the batch_size.

Assumes that the first dimension represents the batch.

##### Args:
• inputs: a tensor of size [batch_size, ...].
• outputs_collections: collection to add the outputs.
• scope: Optional scope for name_scope.
##### Returns:

a flattened tensor with shape [batch_size, k].

##### Raises:
• ValueError: if inputs.shape is wrong.

### tf.contrib.layers.fully_connected(*args, **kwargs)

Adds a fully connected layer.

fully_connected creates a variable called weights, representing a fully connected weight matrix, which is multiplied by the inputs to produce a Tensor of hidden units. If a normalizer_fn is provided (such as batch_norm), it is then applied. Otherwise, if normalizer_fn is None and a biases_initializer is provided then a biases variable would be created and added the hidden units. Finally, if activation_fn is not None, it is applied to the hidden units as well.

##### Args:
• inputs: A tensor of with at least rank 2 and value for the last dimension, i.e. [batch_size, depth], [None, None, None, channels].
• num_outputs: Integer or long, the number of output units in the layer.
• activation_fn: activation function, set to None to skip it and maintain a linear activation.
• normalizer_fn: normalization function to use instead of biases. If normalizer_fn is provided then biases_initializer and biases_regularizer are ignored and biases are not created nor added. default set to None for no normalizer function
• normalizer_params: normalization function parameters.
• weights_initializer: An initializer for the weights.
• weights_regularizer: Optional regularizer for the weights.
• biases_initializer: An initializer for the biases. If None skip biases.
• biases_regularizer: Optional regularizer for the biases.
• reuse: whether or not the layer and its variables should be reused. To be able to reuse the layer scope must be given.
• variables_collections: Optional list of collections for all the variables or a dictionary containing a different list of collections per variable.
• outputs_collections: collection to add the outputs.
• trainable: If True also add variables to the graph collection GraphKeys.TRAINABLE_VARIABLES (see tf.Variable).
• scope: Optional scope for variable_scope.
##### Returns:

the tensor variable representing the result of the series of operations.

##### Raises:
• ValueError: if x has rank less than 2 or if its last dimension is not set.

### tf.contrib.layers.layer_norm(*args, **kwargs)

Adds a Layer Normalization layer from https://arxiv.org/abs/1607.06450.

"Layer Normalization"

Jimmy Lei Ba, Jamie Ryan Kiros, Geoffrey E. Hinton

Can be used as a normalizer function for conv2d and fully_connected.

##### Args:
• inputs: a tensor with 2 or more dimensions. The normalization occurs over all but the first dimension.
• center: If True, subtract beta. If False, beta is ignored.
• scale: If True, multiply by gamma. If False, gamma is not used. When the next layer is linear (also e.g. nn.relu), this can be disabled since the scaling can be done by the next layer.
• activation_fn: activation function, default set to None to skip it and maintain a linear activation.
• reuse: whether or not the layer and its variables should be reused. To be able to reuse the layer scope must be given.
• variables_collections: optional collections for the variables.
• outputs_collections: collections to add the outputs.
• trainable: If True also add variables to the graph collection GraphKeys.TRAINABLE_VARIABLES (see tf.Variable).
• scope: Optional scope for variable_op_scope.
##### Returns:

A Tensor representing the output of the operation.

##### Raises:
• ValueError: if rank or last dimension of inputs is undefined.

### tf.contrib.layers.max_pool2d(*args, **kwargs)

Adds a 2D Max Pooling op.

It is assumed that the pooling is done per image but not in batch or channels.

##### Args:
• inputs: A Tensor of size [batch_size, height, width, channels].
• kernel_size: A list of length 2: [kernel_height, kernel_width] of the pooling kernel over which the op is computed. Can be an int if both values are the same.
• stride: A list of length 2: [stride_height, stride_width]. Can be an int if both strides are the same. Note that presently both strides must have the same value.
• padding: The padding method, either 'VALID' or 'SAME'.
• outputs_collections: The collections to which the outputs are added.
• scope: Optional scope for name_scope.
##### Returns:

A Tensor representing the results of the pooling operation.

##### Raises:
• ValueError: If 'kernel_size' is not a 2-D list

### tf.contrib.layers.one_hot_encoding(*args, **kwargs)

Transform numeric labels into onehot_labels using tf.one_hot.

##### Args:
• labels: [batch_size] target labels.
• num_classes: total number of classes.
• on_value: A scalar defining the on-value.
• off_value: A scalar defining the off-value.
• outputs_collections: collection to add the outputs.
• scope: Optional scope for name_scope.
##### Returns:

one hot encoding of the labels.

### tf.contrib.layers.repeat(inputs, repetitions, layer, *args, **kwargs)

Applies the same layer with the same arguments repeatedly.

  y = repeat(x, 3, conv2d, 64, [3, 3], scope='conv1')
# It is equivalent to:

x = conv2d(x, 64, [3, 3], scope='conv1/conv1_1')
x = conv2d(x, 64, [3, 3], scope='conv1/conv1_2')
y = conv2d(x, 64, [3, 3], scope='conv1/conv1_3')


If the scope argument is not given in kwargs, it is set to layer.__name__, or layer.func.__name__ (for functools.partial objects). If neither __name__ nor func.__name__ is available, the layers are called with scope='stack'.

##### Args:
• inputs: A Tensor suitable for layer.
• repetitions: Int, number of repetitions.
• layer: A layer with arguments (inputs, *args, **kwargs)
• *args: Extra args for the layer.
• **kwargs: Extra kwargs for the layer.
##### Returns:

a tensor result of applying the layer, repetitions times.

##### Raises:
• ValueError: if the op is unknown or wrong.

### tf.contrib.layers.safe_embedding_lookup_sparse(embedding_weights, sparse_ids, sparse_weights=None, combiner=None, default_id=None, name=None, partition_strategy='div')

Lookup embedding results, accounting for invalid IDs and empty features.

The partitioned embedding in embedding_weights must all be the same shape except for the first dimension. The first dimension is allowed to vary as the vocabulary size is not necessarily a multiple of P.

Invalid IDs (< 0) are pruned from input IDs and weights, as well as any IDs with non-positive weight. For an entry with no features, the embedding vector for default_id is returned, or the 0-vector if default_id is not supplied.

The ids and weights may be multi-dimensional. Embeddings are always aggregated along the last dimension.

##### Args:
• embedding_weights: A list of P float tensors or values representing partitioned embedding tensors. The total unpartitioned shape should be [e_0, e_1, ..., e_m], where e_0 represents the vocab size and e_1, ..., e_m are the embedding dimensions.
• sparse_ids: SparseTensor of shape [d_0, d_1, ..., d_n] containing the ids. d_0 is typically batch size.
• sparse_weights: SparseTensor of same shape as sparse_ids, containing float weights corresponding to sparse_ids, or None if all weights are be assumed to be 1.0.
• combiner: A string specifying how to combine embedding results for each entry. Currently "mean", "sqrtn" and "sum" are supported, with "mean" the default.
• default_id: The id to use for an entry with no features.
• name: A name for this operation (optional).
• partition_strategy: A string specifying the partitioning strategy. Currently "div" and "mod" are supported. Default is "div".
##### Returns:

Dense tensor of shape [d_0, d_1, ..., d_{n-1}, e_1, ..., e_m].

##### Raises:
• ValueError: if embedding_weights is empty.

### tf.contrib.layers.separable_convolution2d(*args, **kwargs)

Adds a depth-separable 2D convolution with optional batch_norm layer.

This op first performs a depthwise convolution that acts separately on channels, creating a variable called depthwise_weights. If num_outputs is not None, it adds a pointwise convolution that mixes channels, creating a variable called pointwise_weights. Then, if batch_norm_params is None, it adds bias to the result, creating a variable called 'biases', otherwise it adds a batch normalization layer. It finally applies an activation function to produce the end result.

##### Args:
• inputs: a tensor of size [batch_size, height, width, channels].
• num_outputs: the number of pointwise convolution output filters. If is None, then we skip the pointwise convolution stage.
• kernel_size: a list of length 2: [kernel_height, kernel_width] of of the filters. Can be an int if both values are the same.
• depth_multiplier: the number of depthwise convolution output channels for each input channel. The total number of depthwise convolution output channels will be equal to num_filters_in * depth_multiplier.
• stride: a list of length 2: [stride_height, stride_width], specifying the depthwise convolution stride. Can be an int if both strides are the same.
• padding: one of 'VALID' or 'SAME'.
• activation_fn: activation function, set to None to skip it and maintain a linear activation.
• normalizer_fn: normalization function to use instead of biases. If normalizer_fn is provided then biases_initializer and biases_regularizer are ignored and biases are not created nor added. default set to None for no normalizer function
• normalizer_params: normalization function parameters.
• weights_initializer: An initializer for the weights.
• weights_regularizer: Optional regularizer for the weights.
• biases_initializer: An initializer for the biases. If None skip biases.
• biases_regularizer: Optional regularizer for the biases.
• reuse: whether or not the layer and its variables should be reused. To be able to reuse the layer scope must be given.
• variables_collections: optional list of collections for all the variables or a dictionay containing a different list of collection per variable.
• outputs_collections: collection to add the outputs.
• trainable: whether or not the variables should be trainable or not.
• scope: Optional scope for variable_scope.
##### Returns:

A Tensor representing the output of the operation.

### tf.contrib.layers.stack(inputs, layer, stack_args, **kwargs)

Builds a stack of layers by applying layer repeatedly using stack_args.

stack allows you to repeatedly apply the same operation with different arguments stack_args[i]. For each application of the layer, stack creates a new scope appended with an increasing number. For example:

  y = stack(x, fully_connected, [32, 64, 128], scope='fc')
# It is equivalent to:

x = fully_connected(x, 32, scope='fc/fc_1')
x = fully_connected(x, 64, scope='fc/fc_2')
y = fully_connected(x, 128, scope='fc/fc_3')


If the scope argument is not given in kwargs, it is set to layer.__name__, or layer.func.__name__ (for functools.partial objects). If neither __name__ nor func.__name__ is available, the layers are called with scope='stack'.

##### Args:
• inputs: A Tensor suitable for layer.
• layer: A layer with arguments (inputs, *args, **kwargs)
• stack_args: A list/tuple of parameters for each call of layer.
• **kwargs: Extra kwargs for the layer.
##### Returns:

a Tensor result of applying the stacked layers.

##### Raises:
• ValueError: if the op is unknown or wrong.

### tf.contrib.layers.unit_norm(*args, **kwargs)

Normalizes the given input across the specified dimension to unit length.

Note that the rank of input must be known.

##### Args:
• inputs: A Tensor of arbitrary size.
• dim: The dimension along which the input is normalized.
• epsilon: A small value to add to the inputs to avoid dividing by zero.
• scope: Optional scope for variable_scope.
##### Returns:

The normalized Tensor.

##### Raises:
• ValueError: If dim is smaller than the number of dimensions in 'inputs'.

Aliases for fully_connected which set a default activation function are available: relu, relu6 and linear.