Ellipses are commonly required, and LaTeX natively supplies a fair range (\dots, \cdots, \vdots and \ddots). By using the graphics package, one can change the slope of the \ddots command, as in

$ ... \reflectbox{$\ddots$} ... $
While this works, it is not a recommended way of achieving the desired result (see below). Moreover, LaTeX’s range is not adequate to everyone’s requirements, and at least three packages provide extensions to the set.

The AMSLaTeX bundle provides a range of “semantically-named” ellipses, for use in different situations: \dotsb for use between pairs of binary operators, \dotsc for use between pairs of commas, and so on.

The yhmath package defines an \adots command, which is the analogue of \ddots, sloping forwards rather than backwards. The yhmath package comes with a rather interesting font that extends the standard cmex; details are in the documentation.

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 (doing the same job as yhmath’s \adots, but better).

Documentation of yhmath appears, processed, in the distribution (thus saving you the bother of installing the package before being able to read the documentation). Documentation of mathdots appears at the end the package file itself.

Part of the graphics bundle

This answer last edited: 2013-08-21