Here, we put together some of the things we have learned about so far and will solve the Boolean XOR problem with TensorFlow. In this example, we are going to create a three-layer neural network with sigmoid activation functions. We use log loss as there is only two possible outcomes for out network 0 or 1:

import tensorflow as tf 
# XOR dataset 
XOR_X = [[0, 0], [0, 1], [1, 0], [1, 1]] 
XOR_Y = [[0], [1], [1], [0]] 
 
num_input = 2 
num_classes = 1 
 
# Define model I/O (Placeholders are used to send/get information from graph) 
x_ = tf.placeholder("float", shape=[None, num_input], name='X') 
y_ = tf.placeholder("float", shape=[None, num_classes], name='Y') 
 
# Model structure 
H1 = tf.layers.dense(inputs=x_, units=4, activation=tf.nn.sigmoid) 
H2 = tf.layers.dense(inputs=H1, units=8, activation=tf.nn.sigmoid) 
H_OUT = tf.layers.dense(inputs=H2, units=num_classes, activation=tf.nn.sigmoid) 
 
# Define cost function 
with tf.name_scope("cost") as scope: 
   cost = tf.losses.log_loss( labels=y_, predictions=H_OUT) 
   # Add loss to tensorboard 
   tf.summary.scalar("log_loss", cost) 
 
# Define training ops 
with tf.name_scope("train") as scope: 
   train_step = tf.train.GradientDescentOptimizer(0.1).minimize(cost) 
 
merged_summary_op = tf.summary.merge_all() 
 
# Initialize variables(weights) and session 
init = tf.global_variables_initializer() 
sess = tf.Session() 
# Configure summary to output at given directory 
writer = tf.summary.FileWriter("./logs/xor_logs", sess.graph) 
sess.run(init) 
 
# Train loop 
for step in range(10000): 
   # Run train_step and merge_summary_op 
   _, summary = sess.run([train_step, merged_summary_op], feed_dict={x_: XOR_X, y_: XOR_Y}) 
   if step % 1000 == 0:        
       print("Step/Epoch: {}, Loss: {}".format(step, sess.run(cost, feed_dict={x_: XOR_X, y_: XOR_Y}))) 
       # Write to tensorboard summary 
       writer.add_summary(summary, step)

If you run this script, you should expect to get the following loss graph. We can see the loss has gone to zero that shows the model is trained and has solved the problem. You can repeat this experiment, but now only have one dense layer; you should notice, as we said, that the model is not able to solve the problem

.

To be able to view the graph, you can run the following command in your Command Prompt from the directory where your script is located. This will launch tensorboard for us. We will find out more about tensorboard later in this chapter. 

$ tensorboard --logdir=./logs/xor_logs