I want to illustrate the use of dots in LaTeX.
Here is the output I am looking for:
This is the code I am starting with:
$$ L= \left[ \begin{array}{ccc} 1 & 0 & 0 \quad\cdots\quad0\\ m_{2,1} & 1 & 0 \quad\cdots\quad0\\ m_{3,1} & m_{3,2} & 1 \quad\cdots\quad0\\ \\ \end{array} \right] $$ 
With use of the amsmath package (for bmatrix):
\documentclass{article} \usepackage{amsmath} \begin{document} \[ L= \begin{bmatrix} 1 & 0 & 0 & \cdots & 0\\ m_{2,1} & 1 & 0 & \cdots & 0\\ m_{3,1} & m_{3,2} & 1 & \cdots & 0\\ \vdots & \vdots & \vdots & \ddots & \vdots\\ m_{n,1} & m_{n,2} & \cdots & m_{n,n-1} & 1 \end{bmatrix} \] \end{document} 
\[…\]preferable to$$…$$?\dots(a command defined byamsmath) but your example code and accepted answer demonstrates\cdotsdo you want to change the title?