When the intrinsic algebraic entropy is not really intrinsic

The intrinsic algebraic entropy ent (ϕ) of an endomorphism ϕ of an Abelian group G can be computed using fully inert subgroups of ϕ-invariant sections of G, instead of the whole family of ϕ-inert subgroups. For a class of groups containing the groups of finite rank, as well as those groups which are trajectories of finitely generated subgroups, it is proved that only fully inert subgroups of the group itself are needed to compute ent (ϕ). Examples show how the situation may be quite different outside of this class.