  This note further addresses the global optimization problem for max-plus
linear systems considered in [Automatica 119 (2020) 109104]. Firstly, the
operations between infinity elemens and real numbers involved in the formulas
of solving global optimization problems are explained explicitly. Secondly, the
formula of the greatest lower bound and the criterion of solvability of
globally optimal solutions are simplified. Thirdly, the criterion of uniqueness
of globally optimal solutions and the set of all globally optimal solutions are
presented.
