How do I separate stacks?

[P4v3]

Hey, guys, I guess I'm a bit retarded but I can't figure out how to separate stacks in HOMM5. I mean when I have one stack of, say, 100 archers, how do I split it in two stacks each consisting of 50? Thanks...

[Elvin]

Just press shift and drag the stack you wish to an empty spot.(in the portrait, not in the battlefield though you can still split stacks in the tactics phase.
And it's shameful that Nival didn't document well the game and some functions can only be used with hotkeys...