If you're asking waht I think you're asking, then what you're then looking for is called 'numerical analysis'. Specifically, the grandparent was describing this [1]. Here is an OCW link for a good primer in to various introductory numerical analysis processes for Engineering [2].

[1]: https://en.wikipedia.org/wiki/Gradient_descent

[2]: http://ocw.mit.edu/courses/mechanical-engineering/2-993j-int...