def covariance(self, param_1, param_2):
        """
        Return the covariance between param_1 and param_2.

        :param param_1: ``Parameter`` Instance.
        :param param_2: ``Parameter`` Instance.
        :return: Covariance of the two params.
        """
        param_1_number = self.model.params.index(param_1)
        param_2_number = self.model.params.index(param_2)
        return self.covariance_matrix[param_1_number, param_2_number]
def covariance ( self , param_1 , param_2 ) : param_1_number = self . model . params . index ( param_1 ) param_2_number = self . model . params . index ( param_2 ) return self . covariance_matrix [ param_1_number , param_2_number ]
Return the covariance between param_1 and param_2.

        :param param_1: ``Parameter`` Instance.
        :param param_2: ``Parameter`` Instance.
        :return: Covariance of the two params.