def interpolate_loc(grid, loc):
  """"""
  if len(loc) != 2:
    raise NotImplementedError("Currently only bimixtures are supported; "
                              "len(scale)={} is not 2.".format(len(loc)))
  deg = tf.compat.dimension_value(
      tensorshape_util.with_rank_at_least(grid.shape, 1)[-1])
  if deg is None:
    raise ValueError("Num quadrature grid points must be known prior "
                     "to graph execution.")
  with tf.name_scope("interpolate_loc"):
    if loc is None or loc[0] is None and loc[1] is None:
      return [None]*deg
    # shape: [B, 1, k, deg]
    w = grid[..., tf.newaxis, :, :]
    loc = [
        x[..., tf.newaxis]  # shape: [B, e, 1]
        if x is not None else None for x in loc
    ]
    if loc[0] is None:
      x = w[..., 1, :] * loc[1]                        # shape: [B, e, deg]
    elif loc[1] is None:
      x = w[..., 0, :] * loc[0]                        # shape: [B, e, deg]
    else:
      delta = loc[0] - loc[1]
      x = w[..., 0, :] * delta + loc[1]                # shape: [B, e, deg]
    return [x[..., k] for k in range(deg)]