Extraordinary Symbols

[big brackets, braces, parentheses] [Quantum bra's and ket's] [Wide Tilde] [Bold Greek letters]

[Table of Contents]

big brackets, braces, parentheses

\[
H(x)=\left\{\begin{array}{cl}
	0, & x<0 \\
	1, & x\geq 0
	   \end{array}\right.
\]

Notice the \right. (with a period) to match the \left but without drawing a right brace. This works for ] and \}, too.

\[
A=\left(\begin{array}{ccc|c}
\ast & \ast &      &      \\
\ast & \ast & \ast &      \\
     & \ast & \ast &      \\ \hline
     &      &      & \ast \\
	\end{array}\right)
\]

Quantum bra's and ket's

\newcommand{\bra}[1]{\langle #1|}
\newcommand{\ket}[1]{|#1\rangle}
\newcommand{\braket}[2]{\langle #1|#2\rangle}
\[
\ket{\Psi}=\sum_{i}\ket{\phi_i}\braket{\phi_i}{\Psi}
\]

Note: By defining these with \newcommand, you can use these symbols over and over in your document. If you use these symbols in the text itself, you'll have to surround them with $$.

Wide Tilde

\[
\tilde{1}
\widetilde{1}
\widetilde{12}
\widetilde{123}
\widetilde{1234}
\widetilde{12345}
\]

Notice there appear to be just three different kinds of \widetilde's in addition to the smallest \tilde. \widetilde does not stretch by just the right amount. Somebody should figure that one out, huh?

Bold Greek Letters

Some people prefer to represent vectors in bold-face rather than using a little arrow over the symbol. It's not so clear what you're talking about, but it looks nicer. We're all in Math, and since when did clarity mean anything?

LaTeX completely ignores the \bf in stuff like ${\bf \xi}$, but has \boldmath to get around this. Unfortunately, it only works in text-mode, not math-mode. But (yet another 'but') you can get around this, too, with a little trick or two. Thanks, Michèle, for the code:

% newcommands to make things easier to use later:
\newcommand{\xv}{\mbox{\boldmath$x$}}
\newcommand{\uv}{\mbox{\boldmath$u$}}
\newcommand{\xiv}{\mbox{\boldmath$\xi$}}
...
The vector $\xiv$ represents the location of the centre of
the body, and clearly
\[
  \uv \sim -\log(\xv - \xiv)\ .
\]