A buffer of a given value in a 'flat' (minibatch-indexed) format

def batch_tensor(self, name):
        """ A buffer of a given value in a 'flat' (minibatch-indexed) format """
        if name in self.transition_tensors:
            return tensor_util.merge_first_two_dims(self.transition_tensors[name])
        else:
            return self.rollout_tensors[name]