Center over-long equations between both margins

Question

I understand the reasoning behind the fairly narrow textwidth in a default LaTeX article. 60-80 characters per line and all that. However, I am preparing a document that features many lengthy equations, and it seems silly to me to restrict the equations to fit into the same margins as the text when there's all that whitespace going unused on either side.

I'd like to have equations which are wider than the textwidth do the obvious thing, that is, continue to be centered on the page just like all the other equations, and simply extend into both the left and right margin equally. My equations are unnumbered, so there's no concern about where to put equation numbers.

How might I go about implementing this?

Answer 1

Here's what you want. Please, don't inflict it to your readers

\newsavebox{\overlongequation}
\newenvironment{dontbotheriftheequationisoverlong}
 {\begin{displaymath}\begin{lrbox}{\overlongequation}$\displaystyle}
 {$\end{lrbox}\makebox[0pt]{\usebox{\overlongequation}}\end{displaymath}}

You use it just like displaymath (or \[...\])

\begin{dontbotheriftheequationisoverlong}
1+2+3+4+5+6+7+8+9+10+
11+12+13+14+15+16+17+18+19+20=
210
\end{dontbotheriftheequationisoverlong}

For a solution compatible with other alignment environments, just use a word processor instead of a typesetting system. Seriously: the effect is worse than you can think.

Answer 2

You can use \centerline in combination with the minipage environment for this purpose:

\centerline{
  \begin{minipage}{\linewidth}
    \begin{align*}
      \text{I am very looooooooooooooooooooooooooooooong} &
      \text{Me toooooooooooooooooooooooooooooooooooooooo!}
    \end{align*}
  \end{minipage}
}

The minipage environment embeds a virtual page, containing the math environment align*, as a regular text object, which then gets centered by \centerline.