title: How does reduce_sum() work in tensorflow?
body: <p>I am learning tensorflow, I picked up the following code from the tensorflow website. According to my understanding, axis=0 is for rows and axis=1 is for columns.</p>
  <p>How are they getting output mentioned in comments? I have mentioned output according to my thinking against ##.</p>
  <pre><code>import tensorflow as tf
  
  x = tf.constant([[1, 1, 1], [1, 1, 1]])
  tf.reduce_sum(x, 0)  # [2, 2, 2] ## [3, 3]
  tf.reduce_sum(x, 1)  # [3, 3] ##[2, 2, 2]
  tf.reduce_sum(x, [0, 1])  # 6 ## Didn't understand at all.
  </code></pre>