analytical_engine_cols

\documentclass[preview, border=5pt]{standalone}

\usepackage{tikz}
\usetikzlibrary{shapes.geometric} %Necessari per definir polígons personalitzats

\tikzset{square/.style={regular polygon,regular polygon sides=4,inner sep=4}} %Definició de l'estil "square" (tizk només te "rectangle" per defecte)

\begin{document}
\[
\begin{array}{cccc}
	V_1 & V_2 & V_3 & V_4 \\
	\tikz \node[draw,circle,inner sep=1]{+}; & \tikz \node[draw,circle,inner sep=1]{+}; & \tikz \node[draw,circle,inner sep=1]{+}; & \tikz \node[draw,circle,inner sep=1]{+}; \\
	0 & 0 & 0 & 0 \\
	0 & 0 & 9 & 0 \\
	5 & 7 & 8 & 0 \\
	\tikz \node[draw,rectangle]{$a$}; & \tikz \node[draw,rectangle]{$n$}; & \tikz \node[draw,rectangle]{$x$}; & \tikz \node[draw,square]{}; \\
\end{array}
\]


\end{document}