How to get the parameters of each item?

[summer-liu]

Hi I'm trying to get the parameters of each item in the HIRT model. I found these two functions in OnePOLearner. But they are actually the same and I'm wondering what's the meaning of offset coefficient.

    def get_difficulty(self, item_ids):
        """ Get the difficulties (in standard 1PO units) of an item or a set of items.
        :param item_ids: ids of the requested items
        :return: the difficulties (-offset_coeff)
        :rtype: np.ndarray
        """
        return -self.nodes[OFFSET_COEFFS_KEY].get_data_by_id(item_ids)

    def get_offset_coeff(self, item_ids):
        """ Get the offset coefficient of an item or a set of items.
        :param item_ids: ids of the requested items
        :return: the offset coefficient(s)
        :rtype: np.ndarray
        """
        return self.nodes[OFFSET_COEFFS_KEY].get_data_by_id(item_ids)