The general phenomenon you're noticing here is this: if you're trying to pick some real number x to maximize f(x), you'll start with some particular value of x and keep trying out different values. As long as f(x) seems to be increasing in x, you will increment x by larger and larger amounts. At some point, you shoot past the local maximum, and f(x) decreases. So now you start decrementing x, somewhat more slowly than you were previously incrementing it. Soon x becomes smaller than optimal, and you switch directions again. You'll gradually approach the local maximum, but you actually cross it many times.