Tensor Flow is a machine learning toolkit which recently got published by Google. They published it under Apache License 2.0. Looking at the source code overview, it seems to be mainly C++ with a significant bit of Python.

I guess the abstract of the Whitepaper is a good description what TensorFlow is:

TensorFlow is an interface for expressing machine learning algorithms, and an implementation for executing such algorithms. A computation expressed using TensorFlow can be executed with little or no change on a wide variety of heterogeneous systems, ranging from mobile devices such as phones and tablets up to large-scale distributed systems of hundreds of machines and thousands of computational devices such as GPU cards. The system is flexible and can be used to express a wide variety of algorithms, including training and inference algorithms for deep neural network models, and it has been used for conducting research and for deploying machine learning systems into production across more than a dozen areas of computer science and other fields, including speech recognition, computer vision, robotics, information retrieval, natural language processing, geographic information extraction, and computational drug discovery. This paper describes the TensorFlow interface and an implementation of that interface that we have built at Google. The TensorFlow API and a reference implementation were released as an open-source package under the Apache 2.0 license in November, 2015 and are available at www.tensorflow.org.

The core seems to be written in C++, but it has a Python front end.

By now, I couldn't test much because I just made my GPU machine unusable (while trying to get the GPU General Computing practical software to run...). I'll try to expand this article as soon as possible, but I guess it might take several weeks until I have enough time. Lets see...

## Installation

The documentation about the installation makes a VERY good impression. Better than anything I can write in a few minutes, so ... RTFM 😜

For Linux systems with CUDA and without root privileges, you can install it with:

```
$ pip install https://storage.googleapis.com/tensorflow/linux/gpu/tensorflow-0.5.0-cp27-none-linux_x86_64.whl --user
```

But remember you have to set the environment variable `LD_LIBRARY_PATH`

and
`CUDA_HOME`

. For many configurations, adding the following lines to your
`.bashrc`

will work:

```
export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:/usr/local/cuda/lib64"
export CUDA_HOME=/usr/local/cuda
```

## MNIST

The following code can be used to check if your Tensor Flow installation is
working. You have to have the `get_mnist_data_tf.py`

in the same directory as the following script. I've - more or less - directly
copied it from the tutorial.
Just execute the script below and see if it finishes without throwing errors.

```
#!/usr/bin/env python
from get_mnist_data_tf import read_data_sets
mnist = read_data_sets("MNIST_data/", one_hot=True)
import tensorflow as tf
sess = tf.InteractiveSession()
x = tf.placeholder("float", shape=[None, 784])
y_ = tf.placeholder("float", shape=[None, 10])
W = tf.Variable(tf.zeros([784,10]))
b = tf.Variable(tf.zeros([10]))
sess.run(tf.initialize_all_variables())
y = tf.nn.softmax(tf.matmul(x,W) + b)
cross_entropy = -tf.reduce_sum(y_*tf.log(y))
train_step = tf.train.GradientDescentOptimizer(0.01).minimize(cross_entropy)
for i in range(1000):
batch = mnist.train.next_batch(50)
train_step.run(feed_dict={x: batch[0], y_: batch[1]})
correct_prediction = tf.equal(tf.argmax(y,1), tf.argmax(y_,1))
accuracy = tf.reduce_mean(tf.cast(correct_prediction, "float"))
print(accuracy.eval(feed_dict={x: mnist.test.images,
y_: mnist.test.labels}))
def weight_variable(shape):
initial = tf.truncated_normal(shape, stddev=0.1)
return tf.Variable(initial)
def bias_variable(shape):
initial = tf.constant(0.1, shape=shape)
return tf.Variable(initial)
def conv2d(x, W):
return tf.nn.conv2d(x, W, strides=[1, 1, 1, 1], padding='SAME')
def max_pool_2x2(x):
return tf.nn.max_pool(x, ksize=[1, 2, 2, 1],
strides=[1, 2, 2, 1], padding='SAME')
W_conv1 = weight_variable([5, 5, 1, 32])
b_conv1 = bias_variable([32])
x_image = tf.reshape(x, [-1,28,28,1])
h_conv1 = tf.nn.relu(conv2d(x_image, W_conv1) + b_conv1)
h_pool1 = max_pool_2x2(h_conv1)
W_conv2 = weight_variable([5, 5, 32, 64])
b_conv2 = bias_variable([64])
h_conv2 = tf.nn.relu(conv2d(h_pool1, W_conv2) + b_conv2)
h_pool2 = max_pool_2x2(h_conv2)
W_fc1 = weight_variable([7 * 7 * 64, 1024])
b_fc1 = bias_variable([1024])
h_pool2_flat = tf.reshape(h_pool2, [-1, 7*7*64])
h_fc1 = tf.nn.relu(tf.matmul(h_pool2_flat, W_fc1) + b_fc1)
keep_prob = tf.placeholder("float")
h_fc1_drop = tf.nn.dropout(h_fc1, keep_prob)
W_fc2 = weight_variable([1024, 10])
b_fc2 = bias_variable([10])
y_conv = tf.nn.softmax(tf.matmul(h_fc1_drop, W_fc2) + b_fc2)
cross_entropy = -tf.reduce_sum(y_*tf.log(y_conv))
train_step = tf.train.AdamOptimizer(1e-4).minimize(cross_entropy)
correct_prediction = tf.equal(tf.argmax(y_conv,1), tf.argmax(y_,1))
accuracy = tf.reduce_mean(tf.cast(correct_prediction, "float"))
sess.run(tf.initialize_all_variables())
for i in range(1000):
batch = mnist.train.next_batch(50)
if i%100 == 0:
train_accuracy = accuracy.eval(feed_dict={
x:batch[0], y_: batch[1], keep_prob: 1.0})
print("step %d, training accuracy %g"%(i, train_accuracy))
train_step.run(feed_dict={x: batch[0], y_: batch[1], keep_prob: 0.5})
print("test accuracy %g"%accuracy.eval(feed_dict={
x: mnist.test.images, y_: mnist.test.labels, keep_prob: 1.0}))
```

## Observations

While looking at the MNIST example, I made a couple of observations. Let's begin with the nice parts:

- Tensor Flow has a usable documentation (e.g. The neural network part). Not great, as Lasagne where you have lots of details (e.g. activation functions)
- Seems to be quite easy to use.
- Seems to be well-tested by simply being used in many different projects by Google.
- Just like Theano (and thus Lasagne), Tensor flow has automatic differenciation.

Not sure:

- How easy is it to share trained models? In which format would you do so?
- How easy is it to understand a shared model?
- How easy is it to get something new to Tensor Flow like recurrent layers? (Actually, this seems rather to show that either the Whitepaper is a bit misleading or the documentation / Google search is not that good. In the whitepaper they write something about LTSM models, but I couldn't find any docs about that. Only by manually going through the manual, I found it)

Not so nice:

- Doesn't work with Python 3.
- They don't follow PEP8. I know that there is a Python style guide by Google, but it does not seem to follow that one either. See the next section for some more detailed feedback.
- Just like the other Toolkits, you need CUDA. It doesn't work with OpenCL.

### PEP8

- Whitespace
`W = tf.Variable(tf.zeros([784, 10]))`

should be`W = tf.Variable(tf.zeros([784, 10]))`

. Missing whitespaces happened quite often.- Indent with 2 spaces instead of 4 spaces. The Google guide seems also to use 4.
- Newlines between functions are missing.
- Print statement instead of a print function was used → only Python 2, not Python 3.
- I'm not sure why
`y_`

has the trailing underscore. According to PEP8, a single trailing underscore is used by convention to avoid conflicts with Python keyword. - A mixture of different styles as pointed out on Credric's Blog

## Videos

Starting at 21m 2s:

## Alternatives / Similar software

As I don't really know by now what Tensor Flow is doing, I can't pin-point alternatives. But I have some educated guesses:

- Theano has been around for quite a while and seems to have a similar approach with its computational graph. Enhanced by Lasagne, it is a pretty good alternative when it comes to neural networks. Lasagne has an exceptionally good documentation, but parts of the tutorial could still be improved.
- Caffe was something I recently tried. I didn't like it too much due to the lack of documentation, but it certainly is a big project. Especially when it comes to images.
- I haven't tried, but they look promising:
- Chainer
- MXNet
- CGT
- Torch has a very nice example for a character predictor.

## See also

- Official Website
- github.com/tensorflow
- TensorFlow: Large-Scale Machine Learning on Heterogeneous Distributed Systems
- news.ycombinator.com
- reddit.com/r/programming