Commands argmin and argmax in algorithm

Question

I am trying to use the argmin and the argmax commands that I defined in an algorithm but I keep getting the argument not in the middle but on the right. Does anyone have an idea how to put the argument in the middle.

I declare the operators:

\DeclareMathOperator*{\argmin}{\arg\!\min}
\DeclareMathOperator*{\argmax}{\arg\!\max}

and I use the following packages to write algorithms:

\usepackage[chapter]{algorithm}
\usepackage{algorithmic}

Full algorithm code:

\begin{algorithm}
\begin{algorithmic} 
\STATE some statement here
\WHILE{!stop}
    \STATE $s_{i} = \argmin_{p} \| l_{j} - s_{p} \|$
\ENDWHILE
\end{algorithmic}
\end{algorithm}

Answer 1

$ introduces text style, you will need either \displaystyle or \limits.
(\sum, \int, \lim, … behave in the same manner: Display-style formulas have their super- and subscripts above and below the sign, in text-style formulas they are typeset like normal super- and subscripts.)

If you find both solutions unsatisfying you can define an additional command that has \limitsbuilt in:

\DeclareMathOperator*{\argmin}{argmin}
\DeclareMathOperator*{\argmax}{argmax}
\newcommand*{\argminl}{\argmin\limits}
\newcommand*{\argmaxl}{\argmax\limits}

or with your original macro names having that feature:

\DeclareMathOperator*{\argminOp}{argmin}
\DeclareMathOperator*{\argmaxOp}{argmax}
\newcommand*{\argmin}{\argminOp\limits}
\newcommand*{\argmax}{\argmaxOp\limits}

But than you could just make it without \DeclareMathOperator*:

\newcommand*{\argmin}{\operatornamewithlimits{argmin}\limits}
\newcommand*{\argmax}{\operatornamewithlimits{argmax}\limits}

I have also declared your operators with out the predefined operators \arg and \max as operators are usually in upright font anyway, and then there's no need to re-adjust the space manually (the \!).

Code A (\limits)

\documentclass{book}
\usepackage[chapter]{algorithm}
\usepackage{algorithmic}
\usepackage{amsmath}
\DeclareMathOperator*{\argmin}{argmin}
\DeclareMathOperator*{\argmax}{argmax}
\begin{document}
\begin{algorithm}
\begin{algorithmic} 
\STATE some statement here
\WHILE{!stop}
    \STATE $s_{i} = \argmin\limits_{p} \| l_{j} - s_{p} \|$
\ENDWHILE
\end{algorithmic}
\end{algorithm}
\end{document}

Code B (\displaystyle)

\documentclass{book}
\usepackage[chapter]{algorithm}
\usepackage{algorithmic}
\usepackage{amsmath}
\DeclareMathOperator*{\argmin}{argmin}
\DeclareMathOperator*{\argmax}{argmax}
\begin{document}
\begin{algorithm}
\begin{algorithmic} 
\STATE some statement here
\WHILE{!stop}
    \STATE $\displaystyle s_{i} = \argmin_{p} \| l_{j} - s_{p} \|$
\ENDWHILE
\end{algorithmic}
\end{algorithm}
\end{document}

Code C (built in \limits)

\documentclass{book}
\usepackage[chapter]{algorithm}
\usepackage{algorithmic}
\usepackage{amsmath}
\DeclareMathOperator*{\argmin}{argmin}
\DeclareMathOperator*{\argmax}{argmax}
\newcommand*{\argminl}{\argmin\limits}
\newcommand*{\argmaxl}{\argmax\limits}
\begin{document}
\begin{algorithm}
\begin{algorithmic} 
\STATE some statement here
\WHILE{!stop}
    \STATE $ s_{i} = \argminl_{p} \| l_{j} - s_{p} \|$
\ENDWHILE
\end{algorithmic}
\end{algorithm}
\end{document}

Output

Answer 2

You can use \limits (but this will disrupt the regular skip between consecutive lines):

\documentclass{book}
\usepackage[chapter]{algorithm}
\usepackage{algorithmic}
\usepackage{amsmath}

\DeclareMathOperator*{\argmin}{\arg\!\min}
\DeclareMathOperator*{\argmax}{\arg\!\max}

\begin{document}

\begin{algorithm}
\begin{algorithmic} 
\STATE some statement here
\WHILE{!stop}
    \STATE $s_{i} = \argmin\limits_{p} \| l_{j} - s_{p} \|$
\ENDWHILE
\end{algorithmic}
\end{algorithm}

\end{document}