title: Flatten operation between Dense layers
body: <p>In a Keras implementation, I once saw the two last fully connected layers defined as follows</p>
  
  <pre><code>outX = Dense(300, activation='relu')(outX)
  outX = Flatten()(outX)
  predictions = Dense(1,activation='linear')(outX)
  </code></pre>
  
  <p>Between the two Dense layers, there is Flatten layer, why we must add a Flatten operation between two fully connected layer. Is that always required?</p>