# arg max with constraint notation

I have came across a notation I haven't seen before:

$$\DeclareMathOperator*{\argmax}{\arg\,\max} W_{opt} = \argmax_{|W^TS_WW|=0} |W^TS_BW|$$

I am used to see a variable under $\argmax$, at most I have seen something like $\argmax_{W\in\mathbb{Z}}$.

Is this a way to put constraints? If we don't look at left hand side, it is kind of obscure that we are maximizing w.r.t. $W$. Is this a common notation that I am not aware of?

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 It looks commonplace to me. – user1551 Nov 21 '12 at 19:06