def obfn_fvar(self, i):
        r"""Variable to be evaluated in computing :math:`f_i(\cdot)`,
        depending on the ``fEvalX`` option value.
        """

        return self.X[..., i] if self.opt['fEvalX'] else self.Y
r"""Variable to be evaluated in computing :math:`f_i(\cdot)`,
        depending on the ``fEvalX`` option value.