def write_to_tensorboard(self, tb_writer, tb_tag, step):
    """Writes the value of the tracked metric(s) to tensorboard.

    Args:
      tb_writer (tf.Writer): tensorboard writer to write to.
      tb_tag (str): metrics are written to tb_tag/metric_name(s).
      step (int): the step to use when writing to tensorboard.
    """
    raise NotImplementedError()