title: TensorFlow - Unable to get the value of a variable
body: <p>I'm new to Tensorflow. I have two tensors/tensorflow objects, X &amp; Y which basically are two matrices. I perform some computation on them and want to print their value.</p>
  
  <pre><code>output = tf.reduce_sum(tf.log(tf.exp(tf.matmul(tf.transpose(X), Y))))
  print(output.get_shape()) #Shows ()
  </code></pre>
  
  <p>I want to get the value of <code>output</code>. I'm unable to print it.</p>
  
  <p>Tried doing this :</p>
  
  <pre><code>init = tf.initialize_all_variables()
  sess = tf.Session()
  
  output = tf.reduce_sum(tf.log(tf.exp(tf.matmul(tf.transpose(X), Y))))
  
  print(output.get_shape())
  
  sess.run(init)
  v = sess.run(output)
  print(v)
  </code></pre>
  
  <p>But to no avail ! Throws the following error:</p>
  
  <pre><code>InvalidArgumentError (see above for traceback): You must feed a value for placeholder tensor 'Placeholder' with dtype int32 and shape [100]
  </code></pre>