title: tensorboard doesn't show any graph
body: <p>I am trying to see tensorboard graph.
  I used a example code in tensorflow tutorial(<a href="https://www.tensorflow.org/get_started/mnist/pros" rel="nofollow noreferrer">here</a>)</p>
  
  <p>And I modified a little bit code.</p>
  
  <pre><code>....
  ....
  cross_entropy = tf.reduce_mean(tf.nn.softmax_cross_entropy_with_logits(labels=y_, logits=y_conv))
  train_step = tf.train.AdamOptimizer(1e-4).minimize(cross_entropy)
  correct_prediction = tf.equal(tf.argmax(y_conv,1), tf.argmax(y_,1))
  accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))
  sess.run(tf.global_variables_initializer())
  writer = tf.summary.FileWriter("/home/(my_directory)",sess.graph)
  for i in range(2000):
    batch = mnist.train.next_batch(50)
    if i%100 == 0:
      train_accuracy = accuracy.eval(feed_dict={x:batch[0], y_: batch[1],keep_prob: 1.0})
  print("step %d, training accuracy %g"%(i, train_accuracy))
    else :
      summary =  train_step.run(feed_dict={x: batch[0], y_: batch[1],keep_prob: 0.5})
      writer.add_summary(summary,i)
  print("test accuracy %g"%accuracy.eval(feed_dict={x: mnist.test.images, y_: mnist.test.labels, keep_prob: 1.0}))
  </code></pre>
  
  <p>And in terminal, I typed "tensorboard --logdir="/home/(my_directoory)"</p>
  
  <p>then, in chrome browser, enter the tensorboard through port number 6006.</p>
  
  <p>But, there is no graph as below... what should I do to see my graph?</p>
  
  <p><a href="https://i.stack.imgur.com/2lCjt.png" rel="nofollow noreferrer">enter image description here</a></p>