Recently, Google Brain team released their neural network library 'TensorFlow'. Since Google has a state-of-the-art Deep Learning system, I wanted to explore TensorFlow by trying it out for my first Kaggle submission (Digit Recognition) . After spending few hours getting to know their jargons/APIs, I modified their multilayer convolution neural network and came 140th (with 98.4% accuracy) ... not too shabby for my first submission :D.

If you are interested in outscoring me, apply cross-validation on the below python code or may be consider using ensembles:

Here are few observations based on my experience playing with TensorFlow:

If you are interested in outscoring me, apply cross-validation on the below python code or may be consider using ensembles:

from input_data import * import pandas class DataSets(object): pass mnist = DataSets() df = pandas.read_csv('train.csv') train_images = numpy.multiply(df.drop('label', 1).values, 1.0 / 255.0) train_labels = dense_to_one_hot(df['label'].values) #Add MNIST data from Yan LeCun's website for better accuracy. We hold out test, just for accuracy sake, but could have easily added it :) mnist2 = read_data_sets("/tmp/data/", one_hot=True) train_images = numpy.concatenate((train_images, mnist2.train._images), axis=0) train_labels = numpy.concatenate((train_labels, mnist2.train._labels), axis=0) VALIDATION_SIZE = 5000 validation_images = train_images[:VALIDATION_SIZE] validation_labels = train_labels[:VALIDATION_SIZE] train_images = train_images[VALIDATION_SIZE:] train_labels = train_labels[VALIDATION_SIZE:] mnist.train = DataSet([], [], fake_data=True) mnist.train._images = train_images mnist.train._labels = train_labels mnist.validation = DataSet([], [], fake_data=True) mnist.validation._images = validation_images mnist.validation._labels = validation_labels df1 = pandas.read_csv('test.csv') test_images = numpy.multiply(df1.values, 1.0 / 255.0) numTest = df1.shape[0] test_labels = dense_to_one_hot(numpy.repeat([1], numTest)) mnist.test = DataSet([], [], fake_data=True) mnist.test._images = test_images mnist.test._labels = test_labels import tensorflow as tf sess = tf.InteractiveSession() x = tf.placeholder("float", [None, 784]) # x is input features W = tf.Variable(tf.zeros([784,10])) # weights b = tf.Variable(tf.zeros([10])) # bias y_ = tf.placeholder("float", [None,10]) # y' is input labels #Weight Initialization 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) # Convolution and Pooling 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') # First Convolutional Layer 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) # Second Convolutional Layer 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) # Densely Connected Layer 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) # Dropout keep_prob = tf.placeholder("float") h_fc1_drop = tf.nn.dropout(h_fc1, keep_prob) # Readout Layer W_fc2 = weight_variable([1024, 10]) b_fc2 = bias_variable([10]) y=tf.nn.softmax(tf.matmul(h_fc1_drop, W_fc2) + b_fc2) cross_entropy = -tf.reduce_sum(y_*tf.log(y)) train_step = tf.train.AdamOptimizer(1e-4).minimize(cross_entropy) tf.initialize_all_variables().run() for i in range(20000): batch = mnist.train.next_batch(50) train_step.run(feed_dict={x: batch[0], y_: batch[1], keep_prob: 0.5}) correct_prediction = tf.equal(tf.argmax(y,1), tf.argmax(y_,1)) accuracy = tf.reduce_mean(tf.cast(correct_prediction, "float")) print "test accuracy %g"%accuracy.eval(feed_dict={x: mnist2.test.images, y_: mnist2.test.labels, keep_prob: 1.0}) prediction = tf.argmax(y,1).eval(feed_dict={x: mnist.test.images, keep_prob: 1.0}) f=open('prediction.txt','w') s1='\n'.join(str(x) for x in prediction) f.write(s1) f.close()The above script assumes that you have downloaded train.csv and test.csv from Kaggle's website, input_data.py from TensorFlow's website and installed pandas/TensorFlow.

Here are few observations based on my experience playing with TensorFlow:

- TensorFlow
**does not have an optimizer**: - TensorFlow statically maps an high-level expression (for example "matmul") to a predefined low-level operator (for example: matmul_op.h) based on whether you are using CPU or GPU enabled TensorFlow. On other hand, SystemML compiles a matrix multiplication expression (X %*% y) into one of many matrix-multiplication related physical operators using a sophisticated optimizer that adapts to the underlying data and cluster characteristics.
- Other popular open-source neural network libraries are Caffe, Theano and Torch.
- TensorFlow is
**a parallel, but not a distributed system**: - It does parallelize its computation (across CPU cores and also across GPUs):
- Google has released only the single-node version and kept distributed version in-house. This means that the open-sourced version does not have a parameter server.
- TensorFlow is
**easy to use, but difficult to debug**: - I like TensorFlow's Python API and if the script/data/parameters are all correct, it works absolutely fine :)
- But, if something fails, the error messages thrown by TensorFlow are difficult to decipher. This is because the error messages point to a generated physical operator (for example: tensorflow.python.framework.errors.InvalidArgumentError: ReluGrad input), not to the line of code in the Python program.
- TensorFlow is
**slow to train and not yet robust enough**: - Here are some initial numbers by Alex Smola comparing TensorFlow to other open-source deep learning systems: