seek only a function that calculates the power of an army at balance, that is, when your army is as good as the enemy army
I don't quite understand what you are saying. My goal is to calculate army power, but I can only calculate if my opponents army is about equal to my army. Don't I need to be able to calculate army power in order to do affirm if the two armies balanced?
Also, the number of combat rounds would be a function of my power, enemy power, my HP, and enemy HP. So you should be able to build a function that just calls those four instead of adding a new variable.
As a teacher, I'm interested in seeing if something can be done, but I'm not optimistic to be honest.