## Hypertext Help with LaTeX

### Delimiters

Delimiters are objects which act logically like parentheses. These can be used only in math mode.

The delimiters recognized by LaTeX include

`(`(left parenthesis)`)`(right parenthesis)`[`(left bracket)`]`(right bracket)`\{`(left brace)`\}`(right brace)`|`(vertical line)`\vert`(vertical line)`\|`(double vertical lines)`\Vert`(double vertical lines)`/`(slash)`\backslash`(backslash)`\langle`(left angle bracket)`\rangle`(right angle bracket)`\uparrow`(uparrow)`\downarrow`(down arrow)`\updownarrow`(up/down arrow)

### Making delimiters the right size

Delimiters in formulas should be big enough to "fit" around
the formulas they delimit (for example arround arrays). To
obtain "stretchable" delimiters (LaTeX makes them the
appropriate size) type a `\left` or `\right`
command before the delimiter. `\left` and
`\right` commands must come in matching pairs, although
the delimiters themselves need not be the same. Thus,

\left \{ ... \right \[

produces a legal pair. In cases where only one delimiter is
desired, it is possible to make the matching delimiter
"invisible" by typing a period (`.`) after the command, i.e.,
`\left.` or `\right.`.

In an eqnarray environment the
matching `\left` and `\right` cannot be split
between lines and it may be necessary to use an "invisible"
`\right.` and `\left.` to terminate and begin
parts on different lines. In this case a second problem may
arise, since the size of the delimiters will be chosen only for
the **local part**, so that the size of the
**visible** "left" and "right" delimiters might not
match. The solution is to trick LaTeX into thinking that both
parts have the same vertical height. This can be done by
placing a strut, that is a zero-width
`\rule`. It can also be
accomplished with the `\vphantom` command, which I have
not found documented, but which appears to work.

\vphantom{construct}

creates a zero-width object with the height of
`construct`. The argument can contain things such as
`\frac` or the
variable size math symbols and
should be chosen according to what is in the section with the
delimiter you want to match.

### Some examples

#### A six-j symbol

\[ \left\{ \begin{array}{ccc} a & b & c \\ d & e & f \end{array} \right\} \]

This should be displayed something like (insofar as it can be rendered in "ASCII art"):

( a b c ) - - ( d e f )

Note that the `\[ ... \]` set this off as
Display Math, and that the
Array Environment is used to generate
the three centered columns inside the braces.

#### A "multiple choice" equation

\[ f(x) = \left\{ \begin{array}{l} 0, x < 0 \\ 1, x = 0 \\ 2, x > 0 \end{array} \right. \]

will be displayed as

( 0, x < 0 f(x) = - 1, x = 0 ( 2, x > 0

Note that the "invisible" `\right` delimiter is
specified using a "period".

See also Math Formulas, Math Symbols

- Binary and relational operators
- Math formulas
- Arrays
- Arrows
- Variable size symbols (sums, integrals, etc.)

Back to the LaTeX Table of Contents

Revised 28 Nov 1995.