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Optimization (contrib)

[TOC]

opt: A module containing optimization routines.

Other Functions and Classes

class tf.contrib.opt.ExternalOptimizerInterface {#ExternalOptimizerInterface}

Base class for interfaces with external optimization algorithms.

Subclass this and implement _minimize in order to wrap a new optimization algorithm.

ExternalOptimizerInterface should not be instantiated directly; instead use e.g. ScipyOptimizerInterface.

tf.contrib.opt.ExternalOptimizerInterface.__init__(loss, var_list=None, equalities=None, inequalities=None, **optimizer_kwargs) {#ExternalOptimizerInterface.init}

Initialize a new interface instance.

Args:
  • loss: A scalar Tensor to be minimized.
  • var_list: Optional list of Variable objects to update to minimize loss. Defaults to the list of variables collected in the graph under the key GraphKeys.TRAINABLE_VARIABLES.
  • equalities: Optional list of equality constraint scalar Tensors to be held equal to zero.
  • inequalities: Optional list of inequality constraint scalar Tensors to be kept nonnegative.
  • **optimizer_kwargs: Other subclass-specific keyword arguments.

tf.contrib.opt.ExternalOptimizerInterface.minimize(session=None, feed_dict=None, fetches=None, step_callback=None, loss_callback=None) {#ExternalOptimizerInterface.minimize}

Minimize a scalar Tensor.

Variables subject to optimization are updated in-place at the end of optimization.

Note that this method does not just return a minimization Op, unlike Optimizer.minimize(); instead it actually performs minimization by executing commands to control a Session.

Args:
  • session: A Session instance.
  • feed_dict: A feed dict to be passed to calls to session.run.
  • fetches: A list of Tensors to fetch and supply to loss_callback as positional arguments.
  • step_callback: A function to be called at each optimization step; arguments are the current values of all optimization variables flattened into a single vector.
  • loss_callback: A function to be called every time the loss and gradients are computed, with evaluated fetches supplied as positional arguments.

class tf.contrib.opt.MovingAverageOptimizer {#MovingAverageOptimizer}

Optimizer wrapper that maintains a moving average of parameters.

tf.contrib.opt.MovingAverageOptimizer.__init__(opt, average_decay=0.9999, num_updates=None, sequential_update=True) {#MovingAverageOptimizer.init}

Construct a new MovingAverageOptimizer.

Args:
  • opt: A tf.Optimizer that will be used to compute and apply gradients.
  • average_decay: Float. Decay to use to maintain the moving averages of trained variables. See tf.train.ExponentialMovingAverage for details.
  • num_updates: Optional count of number of updates applied to variables. See tf.train.ExponentialMovingAverage for details.
  • sequential_update: Bool. If False, will compute the moving average at the same time as the model is updated, potentially doing benign data races. If True, will update the moving average after gradient updates.

tf.contrib.opt.MovingAverageOptimizer.apply_gradients(grads_and_vars, global_step=None, name=None) {#MovingAverageOptimizer.apply_gradients}

tf.contrib.opt.MovingAverageOptimizer.compute_gradients(loss, var_list=None, gate_gradients=1, aggregation_method=None, colocate_gradients_with_ops=False, grad_loss=None) {#MovingAverageOptimizer.compute_gradients}

Compute gradients of loss for the variables in var_list.

This is the first part of minimize(). It returns a list of (gradient, variable) pairs where "gradient" is the gradient for "variable". Note that "gradient" can be a Tensor, an IndexedSlices, or None if there is no gradient for the given variable.

Args:
  • loss: A Tensor containing the value to minimize.
  • var_list: Optional list of tf.Variable to update to minimize loss. Defaults to the list of variables collected in the graph under the key GraphKey.TRAINABLE_VARIABLES.
  • gate_gradients: How to gate the computation of gradients. Can be GATE_NONE, GATE_OP, or GATE_GRAPH.
  • aggregation_method: Specifies the method used to combine gradient terms. Valid values are defined in the class AggregationMethod.
  • colocate_gradients_with_ops: If True, try colocating gradients with the corresponding op.
  • grad_loss: Optional. A Tensor holding the gradient computed for loss.
Returns:

A list of (gradient, variable) pairs. Variable is always present, but gradient can be None.

Raises:
  • TypeError: If var_list contains anything else than Variable objects.
  • ValueError: If some arguments are invalid.

tf.contrib.opt.MovingAverageOptimizer.get_name() {#MovingAverageOptimizer.get_name}

tf.contrib.opt.MovingAverageOptimizer.get_slot(var, name) {#MovingAverageOptimizer.get_slot}

Return a slot named name created for var by the Optimizer.

Some Optimizer subclasses use additional variables. For example Momentum and Adagrad use variables to accumulate updates. This method gives access to these Variable objects if for some reason you need them.

Use get_slot_names() to get the list of slot names created by the Optimizer.

Args:
  • var: A variable passed to minimize() or apply_gradients().
  • name: A string.
Returns:

The Variable for the slot if it was created, None otherwise.

tf.contrib.opt.MovingAverageOptimizer.get_slot_names() {#MovingAverageOptimizer.get_slot_names}

Return a list of the names of slots created by the Optimizer.

See get_slot().

Returns:

A list of strings.

tf.contrib.opt.MovingAverageOptimizer.minimize(loss, global_step=None, var_list=None, gate_gradients=1, aggregation_method=None, colocate_gradients_with_ops=False, name=None, grad_loss=None) {#MovingAverageOptimizer.minimize}

Add operations to minimize loss by updating var_list.

This method simply combines calls compute_gradients() and apply_gradients(). If you want to process the gradient before applying them call compute_gradients() and apply_gradients() explicitly instead of using this function.

Args:
  • loss: A Tensor containing the value to minimize.
  • global_step: Optional Variable to increment by one after the variables have been updated.
  • var_list: Optional list of Variable objects to update to minimize loss. Defaults to the list of variables collected in the graph under the key GraphKeys.TRAINABLE_VARIABLES.
  • gate_gradients: How to gate the computation of gradients. Can be GATE_NONE, GATE_OP, or GATE_GRAPH.
  • aggregation_method: Specifies the method used to combine gradient terms. Valid values are defined in the class AggregationMethod.
  • colocate_gradients_with_ops: If True, try colocating gradients with the corresponding op.
  • name: Optional name for the returned operation.
  • grad_loss: Optional. A Tensor holding the gradient computed for loss.
Returns:

An Operation that updates the variables in var_list. If global_step was not None, that operation also increments global_step.

Raises:
  • ValueError: If some of the variables are not Variable objects.

tf.contrib.opt.MovingAverageOptimizer.swapping_saver(var_list=None, name='swapping_saver', **kwargs) {#MovingAverageOptimizer.swapping_saver}

Create a saver swapping moving averages and variables.

You should use this saver during training. It will save the moving averages of the trained parameters under the original parameter names. For evaluations or inference you should use a regular saver and it will automatically use the moving averages for the trained variable.

You must call this function after all variables have been created and after you have called Optimizer.minimize().

Args:
  • var_list: List of variables to save, as per Saver(). If set to None, will save all the variables that have been created before this call.
  • name: The name of the saver.
  • **kwargs: Keyword arguments of Saver().
Returns:

A tf.Saver object.

Raises:
  • RuntimeError: If apply_gradients or minimize has not been called before.

class tf.contrib.opt.ScipyOptimizerInterface {#ScipyOptimizerInterface}

Wrapper allowing scipy.optimize.minimize to operate a tf.Session.

Example:

vector = tf.Variable([7., 7.], 'vector')

# Make vector norm as small as possible.
loss = tf.reduce_sum(tf.square(vector))

optimizer = ScipyOptimizerInterface(loss, options={'maxiter': 100})

with tf.Session() as session:
  optimizer.minimize(session)

# The value of vector should now be [0., 0.].

Example with constraints:

vector = tf.Variable([7., 7.], 'vector')

# Make vector norm as small as possible.
loss = tf.reduce_sum(tf.square(vector))
# Ensure the vector's y component is = 1.
equalities = [vector[1] - 1.]
# Ensure the vector's x component is >= 1.
inequalities = [vector[0] - 1.]

# Our default SciPy optimization algorithm, L-BFGS-B, does not support
# general constraints. Thus we use SLSQP instead.
optimizer = ScipyOptimizerInterface(
    loss, equalities=equalities, inequalities=inequalities, method='SLSQP')

with tf.Session() as session:
  optimizer.minimize(session)

# The value of vector should now be [1., 1.].

tf.contrib.opt.ScipyOptimizerInterface.__init__(loss, var_list=None, equalities=None, inequalities=None, **optimizer_kwargs) {#ScipyOptimizerInterface.init}

Initialize a new interface instance.

Args:
  • loss: A scalar Tensor to be minimized.
  • var_list: Optional list of Variable objects to update to minimize loss. Defaults to the list of variables collected in the graph under the key GraphKeys.TRAINABLE_VARIABLES.
  • equalities: Optional list of equality constraint scalar Tensors to be held equal to zero.
  • inequalities: Optional list of inequality constraint scalar Tensors to be kept nonnegative.
  • **optimizer_kwargs: Other subclass-specific keyword arguments.

tf.contrib.opt.ScipyOptimizerInterface.minimize(session=None, feed_dict=None, fetches=None, step_callback=None, loss_callback=None) {#ScipyOptimizerInterface.minimize}

Minimize a scalar Tensor.

Variables subject to optimization are updated in-place at the end of optimization.

Note that this method does not just return a minimization Op, unlike Optimizer.minimize(); instead it actually performs minimization by executing commands to control a Session.

Args:
  • session: A Session instance.
  • feed_dict: A feed dict to be passed to calls to session.run.
  • fetches: A list of Tensors to fetch and supply to loss_callback as positional arguments.
  • step_callback: A function to be called at each optimization step; arguments are the current values of all optimization variables flattened into a single vector.
  • loss_callback: A function to be called every time the loss and gradients are computed, with evaluated fetches supplied as positional arguments.

class tf.contrib.opt.VariableClippingOptimizer {#VariableClippingOptimizer}

Wrapper optimizer that clips the norm of specified variables after update.

This optimizer delegates all aspects of gradient calculation and application to an underlying optimizer. After applying gradients, this optimizer then clips the variable to have a maximum L2 norm along specified dimensions. NB: this is quite different from clipping the norm of the gradients.

Multiple instances of VariableClippingOptimizer may be chained to specify different max norms for different subsets of variables.

This is more efficient at serving-time than using normalization during embedding lookup, at the expense of more expensive training and fewer guarantees about the norms.

tf.contrib.opt.VariableClippingOptimizer.__init__(opt, vars_to_clip_dims, max_norm, use_locking=False, colocate_clip_ops_with_vars=False, name='VariableClipping') {#VariableClippingOptimizer.init}

Construct a new clip-norm optimizer.

Args:
  • opt: The actual optimizer that will be used to compute and apply the gradients. Must be one of the Optimizer classes.
  • vars_to_clip_dims: A dict with keys as Variables and values as lists of dimensions along which to compute the L2-norm. See tf.clip_by_norm for more details.
  • max_norm: The L2-norm to clip to, for all variables specified.
  • use_locking: If True use locks for clip update operations.
  • colocate_clip_ops_with_vars: If True, try colocating the clip norm ops with the corresponding variable.
  • name: Optional name prefix for the operations created when applying gradients. Defaults to "VariableClipping".

Other Methods

tf.contrib.opt.VariableClippingOptimizer.apply_gradients(grads_and_vars, global_step=None, name=None) {#VariableClippingOptimizer.apply_gradients}

tf.contrib.opt.VariableClippingOptimizer.compute_gradients(*args, **kwargs) {#VariableClippingOptimizer.compute_gradients}

tf.contrib.opt.VariableClippingOptimizer.get_slot(*args, **kwargs) {#VariableClippingOptimizer.get_slot}

tf.contrib.opt.VariableClippingOptimizer.get_slot_names(*args, **kwargs) {#VariableClippingOptimizer.get_slot_names}