# How can I make an ellipse above a letter in math mode?

In Jancewicz's 1980 paper Electromagnetism using Bivectors, he introduces a new notation for bivectors: a letter with an ellipse above it, by analogy to the traditional arrow for straight vectors.

The arrow for a straight vector is easy enough: \vec{x}. If I prefer boldface for vectors, that's easy enough too (just redefine \vec as \mathbf).

But there doesn't seem to be any sort of builtin for an "ellipse above" diacritic. How can I create such a thing?

This is my goal:

Extremely boring MWE:

\documentclass{article}
\begin{document}
$\vec{B} = \mathbf{a} \wedge \mathbf{b}$
\end{document}

• This diacritic doesn't seem to be in Unicode; at least I can't find it in the current charts. Can you provide a more precise reference, with page number, preferably online? (I will be happy to submit it to the Unicode committee for consideration.) – barbara beeton Aug 17 at 23:36
• @barbarabeeton I'm not sure it's used outside Jancewicz, but I'd certainly be glad to see it in Unicode! See page 181 here. – Draconis Aug 18 at 1:32

The accents package allows one to define accents. The syntax to define a new accent is \accentset{〈accent〉}{〈symbol〉}.

There is no ellipse in the standard math alphabet. You can get one by horizontally stretching a circle: \hstretch{2}{\circ}. Parameter 2 can be modified; it defines the scale factor. hstretch command is provided by the scalerel package.

\documentclass{article}

\usepackage[single]{accents}
\usepackage{scalerel}

\newcommand*{\ellipse}{\hstretch{2}{\circ}}
\renewcommand*{\vec}[1]{\accentset{\ellipse}{#1}}

\begin{document}

$\vec{B} = a \wedge b$

\end{document}

• My sincere compliments. I was working also on this question :-). – Sebastiano Aug 16 at 8:14