# starred version of \DeclareMathOperator not working

I am using Kile as my LaTeX editor. I have defined a star for DeclareMathOperator but it does show the behavior of \limits, the subscript appears only in the sides rather than below. But using maptop works \item$\mathop{\inf}\limits_x$. The starred version of operator name is also not working as expected. Please tell me if i am missing something.

Here is my code:

\documentclass[a4paper,10pt]{article}
\usepackage[utf8x]{inputenc}
\usepackage{amsfonts}
\usepackage{amsmath}
\usepackage{amsopn}
\DeclareMathOperator*{\argmax}{argmax}                                          % argmax
\DeclareMathOperator*{\argmin}{argmin}

%opening
\title{Convex Optimization - Points to be clarified}
\author{Venkatesh}

\begin{document}

\section*{Convex sets theory}
\begin{enumerate}
\item what is a positive semi definite matrix and positive semdi definite cone $S_+^n = \{X \in S^n | X \succeq 0 \}$ ?
\item what is domain \textbf{dom} $f$ ?
\item$\mathop{\inf}\limits_x$
\item$\argmax{_c^b} f(b)$
\item$\operatorname*{rank}_v(x)$
\end{enumerate}

\end{document}

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Just put \argmax_{c^b} instead of \argmax{_c^b}. –  Ian Thompson Apr 18 '12 at 12:51
Limits in inline formulas are set to the side, by default, and for good reasons. What precisely do you want to get? –  egreg Apr 18 '12 at 12:55
@egreg i never knew this. I am trying to get the subscript in the bottom of the argmin rather than in the side. and i am using only inline mode. is that the issue? –  Venki Apr 18 '12 at 13:46
I just verified that it works fine if i embed them between . –  Venki Apr 18 '12 at 13:56

Let's look at some modifications to your input:

\documentclass[a4paper,10pt]{article}
\usepackage[utf8x]{inputenc}
\usepackage{amsfonts}
\usepackage{amsmath}
% \usepackage{amsopn} % amsmath loads this automatically
\DeclareMathOperator*{\argmax}{argmax}                                          % argmax
\DeclareMathOperator*{\argmin}{argmin}
\DeclareMathOperator{\dom}{\mathbf{dom}}

%opening
\title{Convex Optimization - Points to be clarified}
\author{Venkatesh}

\begin{document}

\section*{Convex sets theory}
\begin{enumerate}
\item what is a positive semidefinite matrix and positive semidefinite cone $S_+^n = \{X \in S^n \mid X \succeq 0 \}$? % \mid, not |;
\item what is domain $\dom f$?
\item$\inf\limits_x$
\item$\argmax_{c^b} f(b)$
\item$\operatorname*{rank}_v(x)$
\end{enumerate}

\end{document}


The \inf operator is predefined. If you want to put the limit under it also in inline formula, put \limits just after it. The same would be true for \argmax; but limits in inline formulas are usually set to the side in order not to make very high or deep lines that would destroy the pagination balance. The \operatorname* defined operators behave just the same as those defined with \DeclareMathOperator*.

Remember never to leave a space before punctuation (unless you're writing in French).

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Thanks a lot, I got it now –  Venki Apr 18 '12 at 14:00