title: tf variable not changing value when input parameters change
body: <p>I was trying to assign a variable <code>y</code> in tensorflow which is to be dependent on <code>x</code>. But, even upon changing the value of <code>x</code>, <code>y</code> doesn't change.</p>
  
  <pre><code>import tensorflow as tf
  
  sess = tf.Session()
  x=tf.Variable(4,name='x')
  
  model = tf.global_variables_initializer()
  
  sess.run(model)
  y=tf.Variable(2*x,name='y')
  
  model = tf.global_variables_initializer()  
  sess.run(model)
  
  sess.run(x)  
  sess.run(tf.assign(x,2))  
  print(sess.run(y))  
  </code></pre>
  
  <p>I am expecting an output <code>4</code>, but I'm getting <code>8</code>. Any help would be appreciated.</p>
  
  <p>Gramercy...</p>