On: Mathematically analyzing sorting algorithms

[crntaylor]

I've got to admit, I don't understand why this article exists. If you're a beginner, the math is too complicated. If you're anything more than a beginner then you already know that bubble sort is O(n^2) and quick sort is O(n log n) and you probably know how to derive it. Who is this aimed at?

[agumonkey → crntaylor]

I know the complexity, at the intuition level, but can't derive them, even after reading this article.