I'm creating a game where players can make an alloy. To make it less predictable and more interesting, I thought that the durability and hardness of an alloy should not be calculated by a simple formula, because it will be extremely easy to find extrema, where alloy have best statistics.

So the questions is, is there any formula for a function where extrema can be found only by investigating all points? Input values will be in percents: 0.0%-100.0%. I think it should look like this: half sound wave