We give a generalization of the Lenstra–Lenstra–Lovász (LLL) lattice-reduction algorithm that is valid for an arbitrary (split, semisimple) reductive group Formula: see text. This can be regarded as “lattice reduction with symmetries.” We make this algorithm explicit for the classical groups Formula: see text, Formula: see text, and for the exceptional group Formula: see text.
Romano et al. (Tue,) studied this question.