tikz.tex

\begin{tikzpicture}
  \node (W) {$W$};
  \node (UW) [below of=W]{$U_W$};
  \node (A) [above of=W, left of=W]{$A$};
  \node (Y) [above of=W, right of=W]{$Y$};
  \node (UY) [right of=Y]{$X(j)$};

  \draw[->] (UW) to node {} (W);
  \draw[->] (W) to node {} (A);
  \draw[->] (W) to node {} (Y);
  \draw[->] (A) to node {} (Y);
  \draw[->] (UY) to node {} (Y);
\end{tikzpicture}