A short circular cylinder carries a uniform magnetization M parallel to its axis. I want to know what the divergence of M is. Using divergence in cylindrical coordinates I get that ∇[itex]\bullet[/itex]M = 0. Now I was pretty sure of this result until I read the following in my book: "∇[itex]\bullet[/itex]H = -∇[itex]\bullet[/itex]M only when the divergence of M vanishes. If you think I'm being pedantic consider the example of a bar magnet - a short cylinder of iron that carries a permanent uniform magnetization M parallel to its axis. In this case there is no free current anywhere, which can lead you to use the above formula. This is however not correct since the divergence of M does not vanish." This is obviously in disagreement with what I found for the short cylinder - can anyone explain what is wrong?