How to define horizontal, vertical and diagonal dots \ldots,\cdots,\vdots and \ddots

To define dots in Latex, use:

  • \ ldots for horizontal dots on the line
  • \ cdots for horizontal dots above the line
  • \ vdots for vertical dots
  • \ ddots for diagonal dots

Here are some examples:

\[\Sigma=\left[ \begin{array}{ccc} \sigma_{11} & \cdots & \sigma_{1n} \\ \vdots & \ddots & \vdots \\ \sigma_{n1} & \cdots & \sigma_{nn} \end{array} \right]\] 
$$
\Sigma=\left[
\begin{array}{ccc}
   \sigma_{11} & \cdots & \sigma_{1n} \\
   \vdots & \ddots & \vdots \\
   \sigma_{n1} & \cdots & \sigma_{nn}
\end{array}
\right]
$$
\[\forall p=1,\ldots,n.\] 
$$\forall p=1,\ldots,n.$$