Attack 100, STR 100, PDEF 100, Variance 15%, rest 0 (even Power).
atk = [attacker.atk - self.pdef / 2, 0].max
self.damage = atk * (20 + attacker.str) / 20
power = skill.power + user.atk * skill.atk_f / 100
rate = 20 + (user.str * skill.str_f / 100)
self.damage = power * rate / 20
Just keep in mind with Power = 0 there is no state remove shock (removal of states through physical damage).