[Tex/LaTex] Which command should I use for displayed equations

amsmathequationsmath-mode

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

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?

Best Answer

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.

Related Solutions

[Tex/LaTex] What to do with this hyperref note on amsmath

You can see a spacing problem with the following example. The two equations have different spacing with hyperref, but the same spacing (as they should) without it:

\documentclass[fleqn]{article}

\usepackage{amsmath}
\usepackage{hyperref}

\begin{document}

This is a test to check the spacing of the equation environment. Too much?
\begin{equation}
a=b
\end{equation}
This is a test to check the spacing of the equation environment.

This is a test to check the spacing of the equation environment. Too much?%
\begin{equation}
a=b
\end{equation}
This is a test to check the spacing of the equation environment.

\end{document}

But this problem is imo not enough to stop using the equation environment. The other math environments produce too much space if the sentence before the displayed math is short:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

This is a test to check the spacing of the equation environment. Too much? Foo.
\begin{equation}
a=b
\end{equation}
This is a test to check the spacing of the equation environment.

This is a test to check the spacing of the align environment. Too much? Foo.
\begin{align}
a=b
\end{align}
This is a test to check the spacing of the align environment.

\end{document}

which is a much more common problem.

[Tex/LaTex] Which command should I use for textual subscripts in math mode

First of all, the problem presents for textual subscripts, such as those used in physics to distinguish between vectors with the same name (say a force) by a subscripted label that should go in upright type. Textual subscripts are used in many other fields.

In what follows, amsmath is assumed.

$W_{\rm total}$ is totally wrong as it relies on a deprecated command that classes don't need to define (and indeed some don't).
$W_{\mathrm{total}}$ is the correct form of the above. Limitations: spaces are gobbled and hyphens become minus signs.
$W_{\textnormal{total}}$ uses the main roman font of the document, no matter the context; the argument is typeset as text at the correct size.
$W_{\mathup{total}}$ (with Ulrike Fischer's definition) has one advantage over \mathrm, since it uses \familydefault, but the same limitations.
$W_{\operatorname{total}}$ is like using a sledgehammer for killing a fly. It's the same as \mathrm, but hyphens don't become minus signs.
$W_{\text{total}}$ might seem ideal, but it changes font according to the context, so the subscript would appear in italics in a theorem statement.

Therefore, form 3 seems the most natural. Notice that braces are not really necessary, except in case 5.

To be honest, for single words \mathrm (or \mathup) is more efficient, as \textnormal uses \mathchoice and typesets four times the subscript in different sizes. However, the overhead is almost negligible with modern machines and uniformity is to be preferred to efficiency, when it doesn't slow the workflow in a significant way.

If, for some reasons, one wants that textual subscripts are typeset in upright type, but keeping the current font family, for instance because some parts of the document use sans serif type also for math (which I don't agree with), a modified version of \textnormal can be used:

\makeatletter
\DeclareRobustCommand{\textnormalf}[1]{% f for "keep the family
  \text{\usefont{\f@encoding}{\f@family}{m}{n}#1}%
}
\makeatother

Here \f@encoding and \f@family are the current output font encoding and font family, as stored by LaTeX at each (text) font change; with font series m and font shape n we're choosing upright medium type.

Of course, a more meaningful name for \textnormalf should be chosen according to its usage and semantics.

Best Answer

Related Solutions

[Tex/LaTex] What to do with this hyperref note on amsmath

[Tex/LaTex] Which command should I use for textual subscripts in math mode

Related Question