Using the code at the end, I was able to create this image.
I would like to add a plot (I'm plotting kernel densities) to each of the nodes on the edge, and move their labels below the plot, such that the plot and label are the same height as the center box.
This would mean, on the left would be a plot with y below the x-axis and on the right would be a plot with u below the x-axis.
Is this possible to do with the matrix structure, and if not, is there an alternate way to create this?
\documentclass[tikz,border=2]{standalone}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{shapes,snakes,calc}
\tikzstyle{connector} = [->,thick]
\begin{document}
\begin{tikzpicture}[x=3in,y=2in]
\tikzstyle{ann} = [draw=none,fill=none,right]
\matrix[nodes={draw, thick, fill=none},
row sep=0.3cm,column sep=0.5cm] {
\node[draw=none,fill=none] (N1) {$ \mathbf{y}$}; &
\node[rectangle, minimum height=0.5in, minimum width = 0.75in] (N2) {Center}; &
\node[draw=none] (N3) {$ \mathbf{u} $};\\
};
\draw [connector] (N1) -- node {} (N2);
\draw [connector] (N2) -- node {} (N3);
\end{tikzpicture}
\end{document}

