Google TensorFlow Tutorial

Tensor Flow
Tensors: n-dimensional arrays
A sequence of tensor operations
Deep learning process are ﬂows of tensors
Vector: 1-D tensor
Matrix: 2-D tensor
Can represent also many machine learning algorithms

A simple ReLU network
a1 b1 c1
a0 b0 c0
w
a1=a0wa,a+b0wb,a+c0wc,a
b1=a0wa,b+b0wb,b+c0wc,b
c1=a0wa,c+b0wb,c+c0wc,c
Apply relu(…) on a1, b1, c1
Slower approach
Per-neuron operation
More efﬁcient approach
Matrix operation

As matrix operations
a0
a1 b1 c1
a0 b0 c0
w
. =
=relu( )
b0 c0 a1 b1 c1
a1a1
=relu( )b1b1
=relu( )c1c1
wa,a
wb,a
wc,a
wa,b
wb,b
wc,b
wa,c
wb,c
wc,c

With TensorFlow
a1 b1 c1
a0 b0 c0
w
out = tf.nn.relu(y)
y = tf.matmul(x, w)
x w
a0 . =b0 c0
wa,a
wb,a
wc,a
wa,b
wb,b
wc,b
wa,c
wb,c
wc,c
a1 b1 c1
=relu( )a1a1
=relu( )b1b1
=relu( )c1c1
import tensorﬂow as tf

Deﬁne Tensors
xa,a
xb,a
xc,a
xa,b
xb,b
xc,b
xa,c
xb,c
xc,c
w
Variable(<initial-value>,
name=<optional-name>)
w = tf.Variable(tf.random_normal([3, 3]), name='w')
y = tf.matmul(x, w)
relu_out = tf.nn.relu(y)
Variable stores the state of current execution
Others are operations

TensorFlow
Code so far deﬁnes a data ﬂow graph
MatMul
ReLU
Variable
x
y = tf.matmul(x, w)
Each variable corresponds to a
node in the graph, not the result
Can be confusing at the beginning

TensorFlow
Code so far deﬁnes a data ﬂow graph
Needs to specify how we
want to execute the graph MatMul
ReLU
Variable
x
Session
Manage resource for graph execution
sess = tf.Session()
y = tf.matmul(x, w)
result = sess.run(relu_out)

Graph
Fetch
Retrieve content from a node
sess = tf.Session()
y = tf.matmul(x, w)
print sess.run(relu_out)
MatMul
ReLU
Variable
x
Fetch
We have assembled the pipes
Fetch the liquid

Graph
sess = tf.Session()
y = tf.matmul(x, w)
sess.run(tf.initialize_all_variables())
InitializeVariable
Variable is an empty node
MatMul
ReLU
Variable
x
Fetch
Fill in the content of a
Variable node

Graph
sess = tf.Session()
y = tf.matmul(x, w)
x = tf.placeholder("ﬂoat", [1, 3])
Placeholder
How about x?
MatMul
ReLU
Variable
x
Fetch
placeholder(<data type>,
shape=<optional-shape>,
name=<optional-name>)
Its content will be fed

Graph
import numpy as np
sess = tf.Session()
y = tf.matmul(x, w)
print sess.run(relu_out, feed_dict={x:np.array([[1.0, 2.0, 3.0]])})
Feed
MatMul
ReLU
Variable
x
FetchPump liquid into the pipe
Feed

Session management
Needs to release resource after use
sess.close()
Common usage
with tf.Session() as sess:
…
Interactive
sess = InteractiveSession()

Prediction
import numpy as np
relu_out = tf.nn.relu(tf.matmul(x, w))
softmax = tf.nn.softmax(relu_out)
print sess.run(softmax, feed_dict={x:np.array([[1.0, 2.0, 3.0]])})
Softmax
Make predictions for n targets that sum to 1

Prediction Difference
import numpy as np
relu_out = tf.nn.relu(tf.matmul(x, w))
softmax = tf.nn.softmax(relu_out)
answer = np.array([[0.0, 1.0, 0.0]])
print answer - sess.run(softmax, feed_dict={x:np.array([[1.0, 2.0, 3.0]])})

Learn parameters: Loss
Deﬁne loss function
Loss function for softmax
softmax_cross_entropy_with_logits(
logits, labels, name=<optional-name>)
labels = tf.placeholder("ﬂoat", [1, 3])
cross_entropy = tf.nn.softmax_cross_entropy_with_logits(
relu_out, labels, name='xentropy')

Learn parameters: Optimization
Gradient descent
class GradientDescentOptimizer
GradientDescentOptimizer(learning rate)
relu_out, labels, name='xentropy')
optimizer = tf.train.GradientDescentOptimizer(0.1)
train_op = optimizer.minimize(cross_entropy)
sess.run(train_op,
feed_dict= {x:np.array([[1.0, 2.0, 3.0]]), labels:answer})
learning rate = 0.1

Iterative update
relu_out, labels, name=‘xentropy')
optimizer = tf.train.GradientDescentOptimizer(0.1)
train_op = optimizer.minimize(cross_entropy)
for step in range(10):
sess.run(train_op,
feed_dict= {x:np.array([[1.0, 2.0, 3.0]]), labels:answer})
Gradient descent usually needs more than one step
Run multiple times

Add parameters for Softmax
…
softmax_w = tf.Variable(tf.random_normal([3, 3]))
logit = tf.matmul(relu_out, softmax_w)
softmax = tf.nn.softmax(logit)
…
logit, labels, name=‘xentropy')
…
Do not want to use only non-negative input
Softmax layer

Add biases
…
w = tf.Variable(tf.random_normal([3, 3]))
b = tf.Variable(tf.zeros([1, 3]))
relu_out = tf.nn.relu(tf.matmul(x, w) + b)
softmax_w = tf.Variable(tf.random_normal([3, 3]))
softmax_b = tf.Variable(tf.zeros([1, 3]))
logit = tf.matmul(relu_out, softmax_w) + softmax_b
softmax = tf.nn.softmax(logit)
…
Biases initialized to zero

Make it deep
…
relu_out = x
num_layers = 2
for layer in range(num_layers):
relu_out = tf.nn.relu(tf.matmul(relu_out, w) + b)
…
Add layers

Visualize the graph
TensorBoard
writer = tf.train.SummaryWriter(
'/tmp/tf_logs', sess.graph_def)
tensorboard --logdir=/tmp/tf_logs

Improve naming, improve visualization
name_scope(name)
Help specify hierarchical names
…
for layer in range(num_layers):
with tf.name_scope('relu'):
relu_out = tf.nn.relu(tf.matmul(relu_out, w) + b)
…
Will help visualizer to better
understand hierarchical relation
Move to outside the loop?

Add name_scope for softmax
Before After

Add regularization to the loss
eg. L2 regularize on the Softmax layer parameters
…
l2reg = tf.reduce_sum(tf.square(softmax_w))
loss = cross_entropy + l2reg
train_op = optimizer.minimize(loss)
…
print sess.run(l2reg)
…
Add it to the loss
Automatic gradient calculation

Use activation as bias
Everything is a tensor

Residual learning
ILSVRC 2015 classiﬁcation task winer
He et al. 2015

Visualize states
Add summaries
scalar_summary histogram_summary
merged_summaries = tf.merge_all_summaries()
results = sess.run([train_op, merged_summaries],
feed_dict=…)
writer.add_summary(results[1], step)

Save and load models
tf.train.Saver(…)
Default will associate with all variables
all_variables()
save(sess, save_path, …)
restore(sess, save_path, …)
Replace initialization
That’s why we need to run initialization
separately

Convolution
conv2d(input, ﬁlter, strides, padding,
use_cudnn_on_gpu=None, name=None)

LSTM
# Parameters of gates are concatenated into one multiply for efﬁciency.
c, h = array_ops.split(1, 2, state)
concat = linear([inputs, h], 4 * self._num_units,True)
# i = input_gate, j = new_input, f = forget_gate, o = output_gate
i, j, f, o = array_ops.split(1, 4, concat)
new_c = c * sigmoid(f + self._forget_bias) + sigmoid(i) * tanh(j)
new_h = tanh(new_c) * sigmoid(o)
BasicLSTMCell

Word2Vec with TensorFlow
# Look up embeddings for inputs.
embeddings = tf.Variable(
tf.random_uniform([vocabulary_size, embedding_size], -1.0, 1.0))
embed = tf.nn.embedding_lookup(embeddings, train_inputs)
# Construct the variables for the NCE loss
nce_weights = tf.Variable(
tf.truncated_normal([vocabulary_size, embedding_size],
stddev=1.0 / math.sqrt(embedding_size)))
nce_biases = tf.Variable(tf.zeros([vocabulary_size]))
# Compute the average NCE loss for the batch.
# tf.nce_loss automatically draws a new sample of the negative labels each
# time we evaluate the loss.
loss = tf.reduce_mean(
tf.nn.nce_loss(nce_weights, nce_biases, embed, train_labels,
num_sampled, vocabulary_size))

Reuse Pre-trained models
Image recognition
Inception-v3
military uniform (866): 0.647296
suit (794): 0.0477196
academic gown (896): 0.0232411
bow tie (817): 0.0157356
bolo tie (940): 0.0145024

Try it on your Android
github.com/tensorflow/tensorflow/tree/master/tensorflow/
examples/android
Uses a Google Inception model to classify camera
frames in real-time, displaying the top results in an
overlay on the camera image.
Tensorflow Android Camera Demo

github.com/nivwusquorum/tensorﬂow-deepq
Reinforcement Learning using Tensor Flow

github.com/asrivat1/DeepLearningVideoGames
Using Deep Q Networks to LearnVideo Game Strategies

github.com/woodrush/neural-art-tf
Neural art

github.com/sherjilozair/char-rnn-tensorﬂow

github.com/jazzsaxmaﬁa/show_and_tell.tensorﬂow

github.com/jikexueyuanwiki/tensorﬂow-zh

Google Brain Residency Program
Learn to conduct deep learning research w/experts in our team
Fixed one-year employment with salary, beneﬁts, ...
Interesting problems,TensorFlow, and access to
computational resources
Goal after one year is to have conducted several research
projects
New one year immersion program in deep learning research

Who should apply?
People with BSc, MSc or PhD, ideally in CS,
mathematics or statistics
Completed coursework in calculus, linear
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Motivated, hard working, and have a strong
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Programming experience

Program Application & Timeline
DEADLINE: January 15, 2016
Thanks for your attention!

Google TensorFlow Tutorial

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Google TensorFlow Tutorial