title: Keras Reshape: total size of the new array must be unchanged
body: <p>I'm trying to use Keras Reshape function API to reshape the output of a glove embedding (4D shape: (?, 9, 20, 100)) down to 3D (?, 9, 2000). However, when I tried Reshape((9, 2000))(text_layer), an error pops up and says total size of the new array must be unchanged, even though 9 * 20 * 100 = 9 * 2000. Any ideas why? Code is attached.</p>
  
  <pre><code>text = Input(shape=(9, news_text.shape[1]), name='text')
  text_layer = Embedding(
      embedding_matrix.shape[0],
      embedding_matrix.shape[1],
      weights=[embedding_matrix],
      input_length=news_text.shape[1]
  )(text)
  text_layer = Reshape((9, text_layer.shape[2] * text_layer.shape[3]))(text_layer)
  </code></pre>