code: def broadcast_impl(self, old_slices, old_shape, new_shape):
      
      new_slice_shape = self.slice_shape(new_shape)
      def tf_fn(x):
        return (tf.zeros(new_slice_shape, dtype=x.dtype) +
                _expand_dims(x, old_shape, new_shape))
      return self.slicewise(tf_fn, old_slices)
docs: Implementation of a broadcast operation.
  
      Args:
        old_slices: LaidOutTensor.
        old_shape: Shape.
        new_shape: Shape.
  
      Returns:
        LaidOutTensor.