def convex_conj(self):
        """Convex conjugate functional of IndicatorLpUnitBall.

        Returns
        -------
        convex_conj : GroupL1Norm
            The convex conjugate is the the group L1-norm.
        """
        conj_exp = conj_exponent(self.pointwise_norm.exponent)
        return GroupL1Norm(self.domain, exponent=conj_exp)