44

In an equation, I want to display three points like "...", but instead of horizontally, they should be diagonally. I'm sure there must be a command to do that, but a google search did not really help.

Any idea?

  • 7
    "\ddots"; see also detexify.kirelabs.org/classify.html – Grigory M Aug 9 '10 at 8:31
  • That's what I was looking for Grigory M. Thank you. Put it in an answer so I can accept it... – Nigu Aug 9 '10 at 8:41
  • I looked in the tables.pdf file provided with texshop, but didn't find this specific command. I'll have a look at your other references... – Nigu Aug 9 '10 at 8:42
  • @Grigory: We have had lots of questions for symbols which were easily resolved by detexify or symbols. I think it is better to answer them and add a link to detexify, symbols or the general questions, than to close them. However, you can open a question on meta to discuss this. – Caramdir Aug 9 '10 at 8:44
  • well, it's proposed as FAQ entry on meta — but while it's not in FAQ, I guess you're right: we'll have to answer such questions – Grigory M Aug 9 '10 at 8:46
21

According to http://www.tex.ac.uk/cgi-bin/texfaq2html?label=mathlips

The mathdots package (besides fixing up the behaviour of (La)TeX \ddots and \vdots when the font size changes) provides an “inverse diagonal” ellipsis \iddots

That is, \iddots is three dots sloping forwards while \ddots is three dots sloping backwards.

  • 1
    Codecogs doesn't support \iddots – SuperJedi224 May 15 '16 at 23:38
7

An alternative to the \iddots (inverse diagonal dots) from the mathdots package:

\makeatletter
\def\Ddots{\mathinner{\mkern1mu\raise\p@
\vbox{\kern7\p@\hbox{.}}\mkern2mu
\raise4\p@\hbox{.}\mkern2mu\raise7\p@\hbox{.}\mkern1mu}}
\makeatother

Then call with \Ddots

-1

It's not perfect but you can use \dots and \cdot and align them using subscript _ and superscript ^ as demonstrated in row 2 below.

You get the vertical dots on row 1 as a bonus since the need to write diagonal dots are typically related to building a "dotted" matrix like in the picture below.

\newcommand{\vertdots}{\underset{\big{\overset{\cdot}{\cdot}}}{\cdot}} 
\newcommand{\diagdots}{_{^{\big\cdot}\cdot _{\big\cdot}}}

\begin{equation*}
A = \begin{bmatrix} 
a           & \dots         & b         \\ 
\vertdots   &  \diagdots    & \vertdots \\
c           & \dots         & d         \\
\end{bmatrix}
\end{equation*}

This produces a matrix that looks like this:

enter image description here

I tried to align the diagonal dots better but didn't succeed. This will be good enough for me.

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