The space before \DeclareMathOperator'ed operator

Question

The code

\documentclass{article}
\usepackage{amsmath}

\DeclareMathOperator\rad{rad}

\begin{document}
The quotient $A/\rad A$ is hopefully semisimple
\end{document}

results in

and the spacing between the solidus and the rad is killing me. Is there a way to make operators get a more sensible spacing in that context?

Answer 1

You can define a slash that uses \mathopen so it does not have space before a \mathop. I would use a specfic command, but you can use \mathcode"8000 to define / this way if you want

\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator\rad{rad}
\mathchardef\origslash\mathcode`\/
\newcommand\mslash{\origslash\mathopen{}}


\begin{document}

$ 1 \mslash 2 $

$ 1 \mslash \rad x $

$ 1 \mslash \log y $

$ 1 \mslash (a+b) $

{\catcode`\/=\active\global\let/\mslash}
\mathcode`\/="8000


$ 2 / 2 $

$ 2 / \rad x $

$ 2 / \log y $

$ 2 / (a+b) $
\end{document}

Answer 2

If you don't want to do "replace all" in your editor, you can try following macros which redefines behavior of the / character in math mode:

\def\specslash{\mathchar`/\futurelet\next\specslashA}
\def\specslashA{\ifx\next\rad \mskip-\thinmuskip \fi}
{\catcode`/=13 \global\let/=\specslash}
\mathcode`\/="8000

Answer 3

You might try the split fraction from xfrac:

\documentclass{article}
\usepackage{amsmath}
\usepackage{xfrac}

\DeclareMathOperator\rad{rad}

\begin{document}
The quotient $\sfrac{A}{\rad A}$ is hopefully semisimple
\end{document}