\documentclass{article}
\usepackage{com.braju.graphicalmodels}
\usepackage{amsmath}
% \special{papersize=40mm,80mm}
% \setlength{\pdfpagewidth}{40mm}
% \setlength{\pdfpageheight}{80mm}
% \usepackage[vcentering,dvips]{geometry}
% \geometry{papersize={80mm,120mm},total={80mm,120mm},margin=0mm}



\catcode`\@=11%

\pagestyle{empty}

\begin{document}
\TeXtoEPS

\LARGE
\psset{unit=10mm,arrowscale=1.5,linewidth=1.5pt}

\begin{pspicture}(0,0)(4,6)
  \SpecialCoor

  \rput(1,1){\GM@node[observed=true]{y}}
  \GM@label[angle=-180]{y}{$\boldsymbol{y}$}

  \rput(3,1){\GM@node[observed=true]{R}}
  \GM@label[angle=0]{R}{$\boldsymbol{R}$}

  \rput(1,3){\GM@node{x}}
  \GM@label[angle=-180]{x}{$\boldsymbol{x}$}
  
  \rput(3,3){\GM@node[observed=true]{W}}
  \GM@label[angle=0]{W}{$\boldsymbol{W}$}
  
  \rput(1,5){\GM@node{z}}
  \GM@label[angle=-180]{z}{$\boldsymbol{z}$}
  
  \rput(3,5){\GM@node{lambda}}
  \GM@label[angle=0]{lambda}{$\lambda$}

  \ncline[arrows=->]{R}{y}
  \ncline[arrows=->]{W}{x}
  \ncline[arrows=->]{x}{y}
  \ncline[arrows=->]{z}{x}
  \ncline[arrows=->]{lambda}{z}

\end{pspicture}

\endTeXtoEPS
\end{document}