# Horizontal bar in matrix to indicate row vector

To indicate that a vector represents a column of a matrix, we can write

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[paper=letterpaper,margin=1.5in]{geometry}
\usepackage{amsmath, amssymb, amsthm}
\begin{document}

$\begin{bmatrix} \vert & \vert \\ \vec{u} & \vec{v} \\ \vert & \vert \end{bmatrix}$

\end{document}


To achieve

How can I do the same to indicate a vector represents a row (looks like )?

Detexify doesn't return anything that looks like what I want (it thinks I'm drawing an underscore).

• welcome to tex.se! please always provide complete small document beginning with \documentclass and \end{document} on the end. see, if [-\; \vec{v}\; - ] gives what you looking for (so far i didn't see such notations for vectors ...) – Zarko Oct 10 '18 at 15:26
• Even without \vert it makes complete sense that a vertical (or horizontal) vector would span multiple columns. – Werner Oct 10 '18 at 15:34
• I added images for reference. @Zarko, what you suggested works for me, but do you know if there's a command similar to \vert but generates a horizontal line so I don't have to add the extra semicolons? As an analogy, I'm looking for a command that is to \vert like what \hdots is to \vdots. – lynshi Oct 11 '18 at 1:42
• no, i don't know. but probably it can be composed from some elements or drawn, for example with use of the package nicematrix. however, your notation is strange. for similar purposes are usually use \dots, \vdots, \ddots etc. – Zarko Oct 11 '18 at 1:57

You can rotate a \vert, so you get the same thickness.

\documentclass{article}
\usepackage{amsmath}
\usepackage{graphicx}

\newcommand{\brows}[1]{%
\begin{bmatrix}
\begin{array}{@{\protect\rotvert\;}c@{\;\protect\rotvert}}
#1
\end{array}
\end{bmatrix}
}
\newcommand{\rotvert}{\rotatebox[origin=c]{90}{$\vert$}}
\newcommand{\rowsvdots}{\multicolumn{1}{@{}c@{}}{\vdots}}

\begin{document}

$\begin{bmatrix} \vert & \vert \\ \vec{u} & \vec{v} \\ \vert & \vert \end{bmatrix} + \brows{a_1^T \\ a_2^T \\ \rowsvdots \\ a_n^T}$

\end{document}