\subtract latex code example

Example 1: subfigure latex

\usepackage{caption}
\usepackage{subcaption}
\begin{document}
\begin{figure}
\begin{subfigure}{.5\textwidth}
  \centering
  % include first image
  \includegraphics[width=.8\linewidth]{log_demo1.png}  
  \caption{Put your sub-caption here}
  \label{fig:sub-first}
\end{subfigure}
\begin{subfigure}{.5\textwidth}
  \centering
  % include second image
  \includegraphics[width=.8\linewidth]{log_demo2.png}  
  \caption{Put your sub-caption here}
  \label{fig:sub-second}
\end{subfigure}

\newline

\begin{subfigure}{.5\textwidth}
  \centering
  % include third image
  \includegraphics[width=.8\linewidth]{log_demo1.png}  
  \caption{Put your sub-caption here}
  \label{fig:sub-third}
\end{subfigure}
\begin{subfigure}{.5\textwidth}
  \centering
  % include fourth image
  \includegraphics[width=.8\linewidth]{log_demo2.png}  
  \caption{Put your sub-caption here}
  \label{fig:sub-fourth}
\end{subfigure}
\caption{Put your caption here}
\label{fig:fig}
\end{figure}

Example 2: vertical dots latex

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