Memo: How to put a character below or under a word?

http://www.gamedev.net/community/forums/topic.asp?topic_id=436284

Use \underset and \overset

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\begin{equation}\label{Eq:formula3}

    \hat{P} = \underset{P}{\text{argmin}}\{F(P)\},

\end{equation}

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You will get