code: def combine_last_two_dimensions(x):
    
    x_shape = common_layers.shape_list(x)
    a, b = x_shape[-2:]
    return tf.reshape(x, x_shape[:-2] + [a * b])
docs: Reshape x so that the last two dimension become one.
  
    Args:
      x: a Tensor with shape [..., a, b]
  
    Returns:
      a Tensor with shape [..., ab]