Return hyperparameters used by your custom Chainer code during training.

def hyperparameters(self):
        """Return hyperparameters used by your custom Chainer code during training."""
        hyperparameters = super(Chainer, self).hyperparameters()

        additional_hyperparameters = {Chainer._use_mpi: self.use_mpi,
                                      Chainer._num_processes: self.num_processes,
                                      Chainer._process_slots_per_host: self.process_slots_per_host,
                                      Chainer._additional_mpi_options: self.additional_mpi_options}

        # remove unset keys.
        additional_hyperparameters = {k: v for k, v in additional_hyperparameters.items() if v}
        hyperparameters.update(Framework._json_encode_hyperparameters(additional_hyperparameters))
        return hyperparameters