latex, multiple panel figure

More at:
https://tex.stackexchange.com/questions/271518/multiple-panel-figure-with-figures-side-by-side/271522

multiple panel figure in latex. The arrangement is partly controlled by "%", unbelievable.

\documentclass{article}
\usepackage{graphicx}
\usepackage{subcaption}

\begin{document}

\begin{figure}
\centering

\begin{subfigure}[t] {0.4\textwidth}
\centering
\includegraphics[width=\linewidth]{FiguresTables/pdf/BY4742.pdf}
  \caption{}
  \label{Figure:fig_a}
\end{subfigure}
%
\begin{subfigure}[t] {0.4\textwidth}
\centering
     \includegraphics[width=\linewidth]{FiguresTables/pdf/sir2.pdf}
  \caption{}
  \label{Figure:fig_b}
\end{subfigure}

\medskip

\begin{subfigure}[t] {0.4\textwidth}
\centering
     \includegraphics[width=\linewidth]{FiguresTables/pdf/fob1.pdf}
  \caption{}
  \label{Figure:fig_c}
\end{subfigure}
%
\begin{subfigure}[t] {0.4\textwidth}
\centering
     \includegraphics[width=\linewidth]{FiguresTables/pdf/hxk2.pdf}
  \caption{}
  \label{Figure:fig_d}
\end{subfigure}


\begin{minipage}[t]{0.4\textwidth}
\caption{Try a multi-panel figure}
\end{minipage}

\end{figure}

\end{document}



See also: subcaption is more recent that subfigure or subfig
https://tex.stackexchange.com/questions/122314/figures-what-is-the-difference-between-using-subfig-or-subfigure