How to add regularizations in TensorFlow?

A few aspects of the existing answer were not immediately clear to me, so here is a step-by-step guide:

1. Define a regularizer. This is where the regularization constant can be set, e.g.:

   regularizer = tf.contrib.layers.l2_regularizer(scale=0.1)
   

2. Create variables via:

       weights = tf.get_variable(
           name="weights",
           regularizer=regularizer,
           ...
       )
   

   Equivalently, variables can be created via the regular weights = tf.Variable(...) constructor, followed by tf.add_to_collection(tf.GraphKeys.REGULARIZATION_LOSSES, weights).

3. Define some loss term and add the regularization term:

   reg_variables = tf.get_collection(tf.GraphKeys.REGULARIZATION_LOSSES)
   reg_term = tf.contrib.layers.apply_regularization(regularizer, reg_variables)
   loss += reg_term
   

   Note: It looks like tf.contrib.layers.apply_regularization is implemented as an AddN, so more or less equivalent to sum(reg_variables).

As you say in the second point, using the regularizer argument is the recommended way. You can use it in get_variable, or set it once in your variable_scope and have all your variables regularized.

The losses are collected in the graph, and you need to manually add them to your cost function like this.

  reg_losses = tf.get_collection(tf.GraphKeys.REGULARIZATION_LOSSES)
  reg_constant = 0.01  # Choose an appropriate one.
  loss = my_normal_loss + reg_constant * sum(reg_losses)

Hope that helps!