[pstricks] Graphe

[Denis Vergès]

Hello,
With this code :
%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\psset{colsep=0.8cm,rowsep=0.8cm}

\begin{psmatrix}[mnode=circle]
			&			&			& A&			&			& \\
			&R$_{1}$	&			&	&			&R$_{8}$	& \\
			&R$_{2}$	&			&	&R$_{9}$	&R$_{10}$	&R$_{11}$\\
R$_{3}$	&R$_{4}$	&R$_{5}$	&	&			&R$_{12}$	&R$_{13}$\\
			&R$_{6}$	&			&	&R$_{14}$	&R$_{15}$	& \\
			&R$_{7}$	&			&	&R$_{16}$	&			& \\
			&			&			&	&			&R$_{17}$	& \\
			&			&			&	&R$_{18}$	&			& \\
			&			&			&B	&			&			& \\
\end{psmatrix}
\psset{linestyle=dashed}
\psset{arrows=->}
\ncline{1,4}{2,2}\ncline{1,4}{2,6}\ncline{2,2}{3,2}
\ncline{2,6}{3,5}\ncline{2,6}{3,6}\ncline{2,6}{3,7}
\ncline{3,2}{4,1}\ncline{3,2}{4,2}\ncline{3,2}{4,3}
\ncline{4,3}{4,2}\ncline{4,1}{5,2}\ncline{4,2}{5,2}
\ncline{5,2}{6,2}\ncline{6,2}{9,4}\ncline{3,5}{5,5}
\ncline{5,5}{6,5}\ncline{6,5}{7,6}\ncline{7,6}{8,5}
\ncline{8,5}{9,4}\ncline{3,6}{4,6} \ncline{4,6}{5,5}
\ncline{3,7}{4,7} \ncline{4,7}{5,6} \ncline{5,6}{7,6}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
all is fine, except in the last row row of R$_{11}$) : when the case  
is empty I have in every place a small circle ?
Why ?
Thanks in advance.
Denis Vergès