random marks in graph using xy-pic

Question

I used xy-pic to draw a graphical model, but strangely enough when I run it, the circle in the downleft corner is always marked with some random marks. It seems to mark the middle of the circle. Does anyone know how to solve this? Would be of great help!

Thanks a lot!

An example of used code is the following:

\begin{figure}[H]
\centerline{     \xymatrix@C=6em@R=2.4em{ 
                   \xy*{\begin{array}{c}s_W,w_1 \\ U_W\end{array}}*\cir<20pt>{}*\cir<22pt>{}\endxy\ar@{<-}[r]|{all \: a}                          & \xy*{\begin{array}{c}s_B,w_1 \\ U_B\end{array}}*\cir<20pt>{}\endxy\ar@{->}[d]|{all \: a \neq a_1}                \\
       \xy*{\begin{array}{c}s_W,b_1 \\ U_W \end{array}}*\cir<20pt>{}\endxy\ar@{<->}[ur]|{all \: a \neq a_1}\ar@{<->}\ar@{->}[u]|{all \: a \neq a_1}  & \xy*{\begin{array}{c}s_B,b_1 \\ U_B\end{array}}*\cir<20pt>{}\endxy\ar@{<->}[lu]|\hole \ar@{<-}\ar@{<-}[l]|{all \: a }  
        }}
\caption{Situation after product update with $a_1$'s draw}\label{fig:a1dpuu}
\end{figure}

Answer 1

You have extra arrows at

....\ar@{<->}\ar@{->}[u]|{all \: a \neq a_1}  & ....

and at

.... [lu]|\hole \ar@{<-}\ar@{<-}[l]|{all \: a }

After removing them we get

\documentclass{article}
\usepackage[all,cmtip]{xy}
\begin{document}
\begin{figure}[H]
\centerline{
\xymatrix@C=6em@R=2.4em{
                   \xy*{\begin{array}{c}s_W,w_1 \\ U_W\end{array}}*\cir<20pt>{}*\cir<22pt>{}\endxy\ar@{<-}[r]|{all \: a}                          & \xy*{\begin{array}{c}s_B,w_1 \\ U_B\end{array}}*\cir<20pt>{}\endxy\ar@{->}[d]|{all \: a \neq a_1}                \\
       \xy*{\begin{array}{c}s_W,b_1 \\ U_W \end{array}}*\cir<20pt>{}\endxy\ar@{<->}[ur]|{all \: a \neq a_1}\ar@{->}[u]|{all \: a \neq a_1}  & \xy*{\begin{array}{c}s_B,b_1 \\ U_B\end{array}}*\cir<20pt>{}\endxy\ar@{<->}[lu]|\hole \ar@{<-}[l]|{all \: a }
        }}
\caption{Situation after product update with $a_1$'s draw}\label{fig:a1dpuu}
\end{figure}
\end{document}

Answer 2

Maybe you want to try the more modern package tikz-cd which gives you more flexibility but easier syntax:

% arara: pdflatex

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{caption}
\usepackage{mathtools}

\begin{document}
\begin{figure}
    \centering
    \begin{tikzcd}[%
        ,cells={nodes={draw, circle, inner sep=-3.5pt}}
        ,column sep=1.5cm
        ,row sep=1.5cm
        ,every arrow/.append style={shorten <= 3pt, shorten >= 3pt}
        ]
    \tikz{\node[draw, circle]{$\begin{array}{c}s_W,w_1 \\ U_W\end{array}$}} \arrow[<->]{dr} & \begin{array}{c}s_B,w_1 \\ U_B\end{array} \arrow{l}[description]{\text{all }a} \arrow{d}[description]{\text{all }a\ne a_1} \arrow[<->]{dl}[description]{\text{all }a\ne a_1}\\
    \begin{array}{c}s_W,b_1 \\ U_W \end{array} \arrow{u}[description, yshift=2pt]{\text{all }a\ne a_1}  \arrow{r}[description]{\text{all }a} & \begin{array}{c}s_B,b_1 \\ U_B\end{array}
    \end{tikzcd}
\caption{Situation after product update with $a_1$'s draw}\label{fig:a1dpuu}
\end{figure}
\end{document}