Short reference for LaTeX/MathJax commands

Question

Some users are not familiar with the LaTeX notations, which is perfectly fine, but it would be better if we could have an FAQ/help page that explains the basic commands, in a similar way to the markdown edit-help.

We should have a short summary of basic LaTeX commands (and link to a more extensive list of commands, if needed).

Answer 1

You can enclose LaTeX math code in $...$ for inline math, and $$...$$ resp. for indented equations.

MathJax supports essentially the commands native to $\LaTeX$ as well as those defined by amsmath and amssymb (with some exceptions in both directions). For a complete list, see the MathJax reference.

I have found these references to be useful:

• Wikipedia LaTeX help
• LaTeX Wikibook, specifically chapters 4.1 and 4.2
• Detexify for looking up symbols

Aside from that, my personal hints (and what I edit most):

• \mathbb{N} for the natural numbers; similar for other such sets.
• \mathcal{L} for calligraphic letters, e.g. languages
• If you prefer left-aligned non-inline formulae, use $\qquad \displaystyle ...$ (in an own paragraph) instead of $$ ... $$.
• \operatorname{name} for long operator names (non-italic letters and spacing).
• \mathrm{name} or \mathsf{name} for dedicated names, such as P and NP (non-italic letters).
• Parentheses around big stuff (e.g. fractions) are usually undersized. Use \left( ... \right) (similar for [ resp. ] and { resp. }) to have them adapt their size accordingly.
• Use \to, \iff and \implies instead of \rightarrow, \Leftrightarrow and \Rightarrow where appropriate (i.e. semantically fitting).
• You can define your own macros. They survive across multiple math environments, so take care not to destroy other posts.
• Use \text{...} when using English in formulae.
• Use \dots instead of ....

Be aware that the spoiler tag (!>) does not support multiple lines -- even inside math formulae! You'll have to write all of your formula in one line when using spoiler tags.

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Examples

Let $a,b \in \mathbb{B}$ and $a \leq b$. Then, $a + b \geq b$.

$$\sum\limits_{i=0}^n i = \frac{n(n+1)}{2}$$

$\qquad\displaystyle \sum_{i=1}^n i = \frac{n(n+1)}{2}$

$$ \lim\limits_{n \to \infty} \frac{1}{n} = 0 $$

$ \max_n f(x) = - \min_n (-f(n)) $

$L = \{ \langle M, w \rangle \mid M \text{ is a TM and } M(w) = 1 \}$

Quicksort runs in $O(n\log n)$ time on average, but in $O(n^2)$ time in the worst case.

$$\begin{align*}
    a_0     &= 1 \\
    a_{n+1} &= 2 \cdot a_n + 3
\end{align*}$$

$$\chi_S(s) = \begin{cases} 
               1 &, s \in S \\
               0 &, s \notin S
             \end{cases}$$

$\begin{pmatrix}
    1 & 2 & 3 \\ 
    4 & 5 & 6 \\ 
    7 & 8 & 9
  \end{pmatrix}$

$\begin{align*}
  S &\to (S)S \mid A \mid \varepsilon \\
  A &\to aA   \mid a
 \end{align*}$

Answer 2

You may use this online graphical tool to create Latex formulas:

http://www.codecogs.com/latex/eqneditor.php