You can generate a few different kinds of matrices in .

$$ \begin{matrix} a_{11} & 0 & \ldots & a_{1n}\\ 0 & a_{22} & \ldots & a_{2n}\\ \vdots & \vdots & \ddots & \vdots\\ 0 & 0 &\ldots & a_{nn} \end{matrix} $$generates

Note that the individual entries are separated by `&`

, each matrix row
ends with a `\\`

, (carriage return) and that,

`\ldots` | elliptical dots |

`\vdots` | vertical dots |

`\ddots` | diagonal dots |

To get vertical lines or parentheses or brackets, etc. around the
entries you can use the `vmatrix`

, `pmatrix`

, or
`bmatrix`

environments.

See the * User's Guide* by Lamport for more details.

Lastly, if you want a matrix with notation on the borders, the \ construct

$$\bordermatrix{\text{corner}&c_1&c_2&\ldots &c_n\cr r_1&a_{11} & 0 & \ldots & a_{1n}\cr r_2& 0 & a_{22} & \ldots & a_{2n}\cr r_3& \vdots & \vdots & \ddots & \vdots\cr r_4& 0 & 0 &\ldots & a_{nn}}$$gives

Note that the entry ``corner'' appears in the corner, so if you don't want anything there you need to put a blank there explicitly.