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tff.learning.reconstruction.Model

Represents a reconstruction model for use in Tensorflow Federated.

tff.learning.reconstruction.Models are used to train models that reconstruct a set of their variables on device, never sharing those variables with the server.

Each tff.learning.reconstruction.Model will work on a set of tf.Variables, and each method should be a computation that can be implemented as a tf.function; this implies the class should essentially be stateless from a Python perspective, as each method will generally only be traced once (per set of arguments) to create the corresponding TensorFlow graph functions. Thus, tff.learning.reconstruction.Model instances should behave as expected in both eager and graph (TF 1.0) usage.

In general, tf.Variables may be either:

  • Weights, the variables needed to make predictions with the model.
  • Local variables, e.g. to accumulate aggregated metrics across calls to forward_pass.

The weights can be broken down into:

  • Global variables: Variables that are allowed to be aggregated on the server.
  • Local variables: Variables that cannot leave the device.

Furthermore, both of these types of variables can be:

  • Trainable variables: These can and should be trained using gradient-based methods.
  • Non-trainable variables: Could include fixed pre-trained layers or static model data.

These variables are provided via:

  • global_trainable_variables
  • global_non_trainable_variables
  • local_trainable_variables
  • local_non_trainable_variables

properties, and must be initialized by the user of the tff.learning.reconstruction.Model.

While training a reconstruction model, global trainable variables will generally be provided by the server. Local trainable variables will then be reconstructed locally. Updates to the global trainable variables will be sent back to the server. Local variables are not transmitted.

All tf.Variables should be introduced in __init__; this could move to a build method more inline with Keras (see https://www.tensorflow.org/api_docs/python/tf/keras/layers/Layer) in the future.

global_non_trainable_variables An iterable of tf.Variable objects, see class comment for details.
global_trainable_variables An iterable of tf.Variable objects, see class comment for details.
input_spec The type specification of the batch_input parameter for forward_pass.

A nested structure of tf.TensorSpec objects, that matches the structure of arguments that will be passed as the batch_input argument of forward_pass. The tensors must include a batch dimension as the first dimension, but the batch dimension may be undefined.

local_non_trainable_variables An iterable of tf.Variable objects, see class comment for details.
local_trainable_variables An iterable of tf.Variable objects, see class comment for details.

Methods

forward_pass

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Runs the forward pass and returns results.

This method should not modify any variables that are part of the model parameters, that is, variables that influence the predictions. Rather, this is done by the training loop.

Args
batch_input A nested structure that matches the structure of Model.input_spec and each tensor in batch_input satisfies tf.TensorSpec.is_compatible_with() for the corresponding tf.TensorSpec in Model.input_spec.
training If True, run the training forward pass, otherwise, run in evaluation mode. The semantics are generally the same as the training argument to keras.Model.__call__; this might e.g. influence how dropout or batch normalization is handled.

Returns
A BatchOutput object.