Math

Write math in LaTeX between dollar signs and it is typeset with KaTeX when the document is read — the same syntax HedgeDoc and HackMD use, so documents written there render the same here.

Inline math#

Wrap an expression in single dollar signs to typeset it inside a sentence:

Einstein's $E = mc^2$ relates mass and energy.

Display math#

Put $$ on a line of its own above and below an expression to show it as a centred block:

$$
x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
$$

A short block can sit on one line: $$x^2 + y^2 = z^2$$.

• A block may not contain blank lines.
• A $$ with no closing $$ (before a blank line, a code fence or the end of a list item or quote) stays plain text, and everything after it renders as normal.
• $$…$$ in the middle of a sentence is shown as a centred block too.

Dollar signs that stay dollars#

Ordinary dollar signs are left alone:

• A closing $ directly followed by a digit or letter is never a delimiter, so prices like $5 and $10 and shell variables like $HOME/$PATH stay text.
• Code is not math: `$x$` and fenced code blocks show their dollar signs as written — as long as no $ earlier on the line opens math that runs into the code span.
• Write \$ for a literal dollar sign anywhere.

A dollar sign followed by a space is read as an opening delimiter, so $ 5 and $ 10 becomes math. Escape those as \$ 5 and \$ 10.

Math in tables#

A | splits a table cell, even inside math. Use \vert or \mid instead:

| Set | Definition |
| --- | --- |
| Evens | $\{ n \mid n \bmod 2 = 0 \}$ |

What's supported#

Everything in KaTeX's list of supported functions: fractions, roots, sums and integrals, matrices, aligned environments, Greek letters, accents, colours and the rest. A few things are deliberately off:

• \href, \url, \includegraphics and the \html… commands are disabled — they show in red as unsupported — so math can never become a link or markup.
• There is no ```math fence, and \(…\) and \[…\] are not delimiters.
• A \def lasts only for the expression it is written in.

Errors#

An expression KaTeX can't parse is shown in red, with the problem as its hover text. The rest of the document renders as normal.

Limits#

To keep a single document from slowing every reader's browser:

• A document typesets at most 1,000 expressions, of up to 10,000 characters each and 50,000 in total. Math past those limits is shown as its source.
• Extreme sizes — a \kern, \raisebox or similar beyond about 50em — are shown as source, and any length above 10em is capped.

Where it renders#

Math is typeset on the document page and in the editor's preview. Raw, .md and link previews show the source, and comments don't render math.