Matrices

You can generate a few different kinds of matrices in .

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

Note that the individual entries are separated by &, each matrix row ends with a \\, (carriage return) and that,

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

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

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.