Dots in the middle of a row

Question

How can I put the dots in the middle of the last line? The following doesn't work.

\documentclass{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage{amsmath,mathtools}
\begin{document}
\begin{align*}
a&=a+a+a+a+a\\
a&=a+a+a+a+a+a+a+a+a+a\\
\vdotswithin{a=a+a+a+a+a+a+a+a+a+a}
\end{align*}
\end{document}

Thank you!

You should use in the last row &\vdotswithin{=}. \vdotswithin just aligns the dots in the middle of the witdth of the argument, that way, after the alignment point & you are aligning the dots to the middle of the equal sign width. — Manuel, Sep 14 '16 at 16:24
In the middle of what? Of the whole last line? You can do \sbox0{$a$} \kern-\wd0 before your \vdotshwithin{..}. — Manuel, Sep 14 '16 at 16:26

score 2 · Accepted Answer · answered Sep 14 '16 at 16:47

2

Don't tell anybody, it's a secret:

\documentclass{scrartcl}

\usepackage{amsmath}

\begin{document}

\begin{align*}
a&=a+a+a+a+a\\
a&=a+a+a+a+a+a+a+a+a+a\\
\multispan{2}\hfill\vdots\hfill
\end{align*}

\end{document}

(I removed whatever unnecessary for the example.)

answered Sep 14 '16 at 16:47

egreg

1,121,712

(+1) I didn't know this one. Thanks! I hope I made good usage in an addendum to my answer. – Bernard Sep 14 '16 at 17:50

Bernard · Answer 2 · 2016-09-14T17:36:53.833

Maybe you want this, based on the eqparbox package:

\documentclass{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage{mathtools, eqparbox}

\newcommand\eqmathbox[2][1]{\eqmakebox[#1]{\ensuremath{\displaystyle#2}}}

\begin{document}

\begin{align*}
  a & =a+a+a+a+a \\
  a & =\eqmathbox[ls]{ a+a+a+a+a+a+a+a+a+a} \\[-1ex]
    & ⋮ within{=}\eqmathbox[ls]{ ⋮ } \\
\end{align*}

\end{document}

Taking advantage of @egreg's secret, the following code produces the same result (note no space must be left in the 3rd row code):

\begin{align*}
a&=a+a+a+a+a\\
a&= a+a+a+a+a+a+a+a+a+a\\[-1ex]
 &\multispan{1}\ensuremath{\vdotswithin{=}}\hfill\vdots\hfill
\end{align*}

score 0 · Answer 3 · edited Apr 13 '17 at 12:35

Taking for instance egreg's definition you can just do in the last line &\negphantom{a}\vdotswithin{a=a+a+a+a+a+a+a+a+a+a}

\makeatletter
\newlength\negph@wd
\DeclareRobustCommand*\negphantom[1]
  {\ifmmode\mathpalette\negph@math{#1}%
   \else\negph@do{#1}\fi}
\newcommand*\negph@math[2]{\negph@do{$#1#2\m@th$}}
\newcommand*\negph@do[1]
  {\settowidth{\negph@wd}{#1}\hspace*{-\negph@wd}}
\makeatother

Dots in the middle of a row

3 Answers3