Math & Science ⇒ Expression like binomial Coefficient with Angle Delimiters

[Richard_B]

I want to typest a binomial coefficient but using angle brackets instead of round parentheses. This notation is used in the book "Counting: The Art of Enumerative Combinatorics" by George E. Martin to denote "n choose r with repetition."

I tried

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$\left\langle\begin{array}{c} n \\ r \end{array}\right\rangle$

but that was too big and didn't look right. I also tried

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$\langle \stackrel{n}{r} \rangle$

but that didn't look right either.

If anyone has a solution to this, please let me know.

[Stefan Kottwitz]

Hi Richard,

welcome to the board!

You could use \genfrac of amsmath and define your own macro.

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\documentclass[a4paper]{article}
\usepackage{amsmath}

\DeclareRobustCommand{\abinom}{\genfrac{\langle}{\rangle}{0pt}{}}

\begin{document}
  \[
    \abinom{n}{r}
  \]
\end{document}

Stefan

[Richard_B]

Hi Stefan,

Thank you. That works perfectly and is exactly what I needed.