message: Added two more examples.
diff: @@ -2831,6 +2831,17 @@ def flatten(x):
  Returns:
  A tensor, reshaped into 1-D
  +
  + Example:
  + ```python
  + >>> b = tf.constant([[1, 2], [3, 4]])
  + >>> b
  + <tf.Tensor: id=102, shape=(2, 2), dtype=int32, numpy=
  + array([[1, 2],
  + [3, 4]], dtype=int32)>
  + >>> tf.keras.backend.flatten(b)
  + <tf.Tensor: id=105, shape=(4,), dtype=int32, numpy=array([1, 2, 3, 4], dtype=int32)>
  + ```
  """
  return array_ops.reshape(x, [-1])
  @@ -2992,6 +3003,19 @@ def stack(x, axis=0):
  Returns:
  A tensor.
  +
  + Example:
  + ```python
  + >>> a = tf.constant([[1, 2],[3, 4]])
  + >>> b = tf.constant([[10, 20],[30, 40]])
  + >>> tf.keras.backend.stack((a, b))
  + <tf.Tensor: id=146, shape=(2, 2, 2), dtype=int32, numpy=
  + array([[[ 1, 2],
  + [ 3, 4]],
  +
  + [[10, 20],
  + [30, 40]]], dtype=int32)>
  + ```
  """
  return array_ops.stack(x, axis=axis)
  