Math & Science ⇒ Vertical alignment of genfrac-derived command within parens

[kpedro88]

I was looking for ways to extend the \binom command to include more than 2 arguments. The formatting of \pmatrix was not satisfying for me, so I came up with a custom command based on \genfrac from amsmath:

Code: Select all

\newcommand\triplet[3]{\left(\genfrac{}{}{0pt}{0}{#1}{\genfrac{}{}{0pt}{0}{#2}{#3}}\right)}

I'm mostly satisfied with how this appears, except that the arguments are not quite vertically centered within the parentheses. Can anyone offer a way to make the arguments vertically centered?

I have attached an example showing \binom and my new command \triplet for comparison.

Code: Select all

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\newcommand\triplet[3]{\left(\genfrac{}{}{0pt}{0}{#1}{\genfrac{}{}{0pt}{0}{#2}{#3}}\right)}

\begin{equation}
\binom{1/3}{-2/3}
\end{equation}

\begin{equation}
\triplet{2/3}{-1/3}{-4/3}
\end{equation}

\end{document}

[Johannes_B]

I would use a different approach.

Code: Select all

\documentclass{article}
\usepackage{mathtools}
\begin{document}

\newcommand\tripler[4][c]{\left(%
	\begin{array}{@{}#1@{}}#2\\#3\\#4%
\end{array}%
\right)%
}

\begin{equation}
\binom{1/3}{-2/3}
\end{equation}

\begin{equation}
\tripler{2/3}{-1/3}{-4/3}
\end{equation}

\begin{equation}
\tripler[r]{2/3}{-1/3}{-4/3}
\end{equation}
\end{document}

[kpedro88]

That's fantastic. Everything aligns perfectly. I'm actually going to replace \binom with the equivalent version of that command just for the alignment. Thanks so much!