title: Tensorflow median value
body: <p>How can I calculate the median value of a list in tensorflow?
  Like </p>
  
  <pre><code>node = tf.median(X)
  </code></pre>
  
  <p>X is the placeholder<br>
  In numpy, I can directly use np.median to get the median value. How can I use the numpy operation in tensorflow?</p>