How to write argmax and argmin

$ \operatorname{arg\,max}_a f(a) \operatorname*{arg\,max}_b f(b)$

Note that the first version is more for inline code, while the second is rather for equation. Naturally, arg min is written analogously. Don't forget to use the amsmath package

For more info see
http://en.wikibooks.org/wiki/LaTeX/Advanced_Mathematics