initialization_trouble.py

import argparse
import numpy as np
import tensorflow as tf

from tensorflow.python.framework.errors import FailedPreconditionError

"""Code for data dependent initialization in Weight Normalization paper:
https://arxiv.org/abs/1602.07868
"""

parser = argparse.ArgumentParser()
parser.add_argument('mode', choices=['standard', 'onebyone'], type=str)
args = parser.parse_args()


def initialize_interdependent_variables(session, vars_list, feed_dict):
    """Initialize a list of variables one at a time, which is useful if
    initialization of some variables depends on initialization of the others.
    """
    vars_left = vars_list
    while len(vars_left) > 0:
        new_vars_left = []
        for v in vars_left:
            try:
                session.run(tf.variables_initializer([v]), feed_dict)
            except FailedPreconditionError:
                new_vars_left.append(v)
        if len(new_vars_left) >= len(vars_left):
            # This can happend if the variables all depend on each other, or more likely if there's
            # another variable outside of the list, that still needs to be initialized.
            raise Exception("Cycle in variable dependencies, or external precondition unsatisfied.")
        else:
            vars_left = new_vars_left


def fully_connected(x,
                    num_outputs,
                    activation_fn=None,
                    init_scale=1.,
                    scope=None,
                    reuse=None):
    with tf.variable_scope(scope, default_name="fully_connected", reuse=reuse):
        # data based initialization of parameters
        V = tf.get_variable(
            'V',
            [int(x.get_shape()[1]), num_outputs],
            tf.float32,
            tf.random_normal_initializer(0, 0.05), trainable=True
        )
        V_norm = tf.nn.l2_normalize(V, [0])
        x_init = tf.matmul(x, V_norm)
        m_init, v_init = tf.nn.moments(x_init, [0])
        scale_init = init_scale / tf.sqrt(v_init + 1e-10)
        g = tf.get_variable('g', dtype=tf.float32, initializer=scale_init, trainable=True)
        b = tf.get_variable('b', dtype=tf.float32, initializer=-m_init * scale_init, trainable=True)

        # use weight normalization (Salimans & Kingma, 2016)
        x = tf.matmul(x, V)
        scaler = g / tf.sqrt(tf.reduce_sum(tf.square(V), [0]))
        x = tf.reshape(scaler, [1, num_outputs]) * x + tf.reshape(b, [1, num_outputs])

        # apply activation_fn
        if activation_fn is not None:
            x = activation_fn(x)
        return x


x = tf.placeholder(tf.float32, [None, 28 * 28])
h1 = fully_connected(x, num_outputs=200)
y = fully_connected(x, num_outputs=10)

session = tf.Session()

if args.mode == 'standard':
    # OPTION 1: Use tensorflow init (throws FailedPreconditionError)
    session.run(tf.global_variables_initializer(), {
        x: np.ones((128, 28 * 28))
    })
elif args.mode == 'onebyone':
    # OPTION 2: Initialize variables one by one
    initialize_interdependent_variables(session, tf.global_variables(), {
        x: np.ones((128, 28 * 28))
    })

# Ideal solution: tf.variables_initializer topologically
#                 sorts variables w.r.t dependency graph,
#                 before initializing.