Which command should I use for displayed equations?

Question

A number of related questions have already been asked about this issue:

• align vs equation
• which is preferable to
• what to do with this hyperref note on amsmath
• and even eqnarray vs align

But I'm still confused by the conflicting suggestions that have been given so far. So I'm trying again.

Which should be the preferred command to produce a displayed equation in my LaTeX documents?

So far the suggestions indicate that one should use \[ ... \], maybe \begin{equation*} ... \end{equation*}, or maybe even the gather* or align* environments from amsmath.

And one should definitely avoid using either $$...$$ or the eqnarray environment.

Now I have to say that, from a language perspective, I have a strong preference for the equation* environment because it is less cryptic than the \[ ... \] notation and it is semantically the most accurate.

So, is it fine to use equation*? Maybe only after loading amsmath? Or should the equation/equation* environment be redefined to something else so that spacing, package support, or whatever is improved?

Answer 1

You should use the environments from amsmath. In practice, equation and align are all you usually need.

• If you have a single equation, use equation. (Or equation* if you don't want it numbered. Most of the other environments below also have similar * variants.)

• If you have a single equation spanning multiple lines, you can either use multline, or use split (inside equation) to have the parts aligned.

• If you have multiple equations and you want them to be aligned, use align (or align*).

• If you simply want to typeset multiple equations independently (with no alignment), use gather.

There are also flalign and alignat, for some special cases. See the Short Math Guide for LaTeX or texdoc amsldoc (PDF) for more documentation on these environments.

\[ simply says "set the following in a math display", like plain TeX 's $$ (which you should not use), and is equivalent to displaymath. You can use it if you want an unnumbered equation and are too lazy to type (not good practice, semantically speaking), or, I guess, when you're simply "displaying" some long bit of mathematics that isn't an actual equation. And never use eqnarray.

Answer 2

The equation environment cannot be compared to \[...\] because it's numbered. The equivalent to \[...\] is the displaymath environment. So you may use that for unnumbered equations.

Though amsmath redefines equation to allow a starred version.

As using amsmath is always recommended, using equation and equation* might be more consistent.

$$ and eqnarray are out of question, whereas gather, align and the like are designed for multi-line formulas, I wouldn't misuse them for single-line equations.

Answer 3

full disclosure: i have a built-in bias towards amsmath.

although in most cases, \[...\] is comparable to the equation* environment, there's one place where it isn't. if you are using an ams document class, a qed marker is automatically placed by the \end{proof}. if the proof ends with some other environment -- a display or list -- the qed marker is placed all by itself on the line below.

if your proof ends with an unnumbered display, you probably want the qed marker to be placed on the same line as the display. \qedhere, placed just before the \end{...} environment for the display will move the qed marker up into the scope of the display. but it won't work for \[...\], and it won't work for \begin{eqnarray}...\end{eqnarray}. (it will also work for \end{enumerate} and \end{itemize}, but that wasn't the question here.)