expression below argmax

Question

In some places in my document I have used the following (and it works quite well):

documentclass{article}
usepackage{amsmath}
DeclareMathOperator*{argmax}{argmax} % thin space, limits underneath in displays

begin{document}

[z = argmax_x f(x)]

end{document}

However, when I try to use something like this:

documentclass{article}
usepackage{amsmath}
DeclareMathOperator*{argmax}{argmax} % thin space, limits underneath in displays

begin{document}

begin{tabular}{c l}
        $z = argmax_x f(x)$ 
        $z = argmax_{x in mathcal{X}} f(x)$
    end{tabular}

end{document}

It does not work anymore. It seems that tabular is somehow to blame here.

UPDATE2:
Well, it was clearly because I was using inline math ($). Thanks David!

David Carlisle · Accepted Answer

It isn't clear what you mean by "not work" the output is as I expect.

documentclass{article}

usepackage{amsmath}
DeclareMathOperator*{argmax}{argmax} % thin space, limits underneath in displays

begin{document}

a
[z = argmax_x f(x)]

b
[z = argmax_{x in mathcal{X}} f(x)]

end{document}

Updated question shows it is just an issue of display or inline setting:

documentclass{article}

usepackage{amsmath}
DeclareMathOperator*{argmax}{argmax} % thin space, limits underneath in displays

begin{document}

a
[z = argmax_x f(x)]

b
[z = argmax_{x in mathcal{X}} f(x)]

a2
$z = argmax_x f(x)$

b2
$z = argmax_{x in mathcal{X}} f(x)$

a3 (don't do this)
$z = argmaxlimits_x f(x)$

b3 (or this)
$z = argmaxlimits_{x in mathcal{X}} f(x)$

c
begin{align*}
z &= argmax_x f(x)
z &= argmax_{x in mathcal{X}} f(x)
end{align*}

end{document}

stackoverflowuser2010 · Answer

Try using underset{belowtext}{text}.
Note below that:

mathrm is for using non-italics Roman font in math mode.
, is for adding a thin space

z = underset{x}{mathrm{argmax}}, f(x)

2 Answers