3

Compiling the following tex lines 

\documentclass{amsart}
\usepackage[all]{xy}
\def\rddots#1{\cdot^{\cdot^{\cdot^{#1}}}}    

\begin{document}

\[ 
\xymatrix@-1.75pc{
\overset{}{\bullet} & & \overset{}{\bullet} 
& &\ldots & & 
\overset{}{\bullet} & & \overset{}{\bullet}
& & \overset{}{\bullet} & &\overset{}{\bullet} 
& &\ldots & &  
\overset{}{\bullet} & &\overset{}{\bullet}   \\ 
& \ar@{-}[ul] \overset{}{\bullet} \ar@{-}[ur] 
& & & & & & \ar@{-}[ul] \overset{}{\bullet} \ar@{-}[ur] 
& & & & \ar@{-}[ul] \overset{}{\bullet} \ar@{-}[ur]
& & & & & & 
\ar@{-}[ul] \overset{}{\bullet} \ar@{-}[ur] &   \\ 
&  & \ddots & & & & &  \vdots & &  & & 
\vdots & & & & & \rddots
& &  \\ 
&  & & \overset{}{\bullet}& & & & 
\overset{}{\bullet} 
& & & & \overset{}{\bullet}& & & & 
\overset{}{\bullet} 
& & &   \\ 
&  & & & &  \ar@{-}[ull]\overset{}{\bullet}\ar@{-}[urr] 
& & & & & & & & \ar@{-}[ull]\overset{}{\bullet} \ar@{-}[urr]
& & & & &  \\ 
&  & & & & & & & &  \ar@{-}[ullll] \overset{}{\bullet}
\ar@{-}[urrrr]
& & & & & & & & & \\  }
\] 

\end{document}

produces this tree

tree

but I am getting an error 

! Misplaced alignment tab character &.
<argument> ...veryentry@ \cdot ^{\cdot ^{\cdot ^{&
                                                  }}} 
l.34     & & & & & & & & & \\  }

and I am not sure how to resolve it. The problem is coming from rddots. Any assistance to address this would be appreciated.

Mee Seong Im
  • 209

1 Answers1

3

Instead of doing that command to obtain the dots, rotate the normal \ddots. Load graphicx and make use of \rotatebox{90}{$\ddots$} to rotate by 90 degrees. Observe that $\ddots$ is passed in math mode since the second argument of \rotatebox{}{} does not imply to math mode.

\usepackage{graphicx}
\newcommand{\rddots}{\rotatebox{90}{$\ddots$}}

enter image description here

\documentclass{amsart}
\usepackage[all]{xy}
\usepackage{graphicx} % added
\begin{document}

\[ 
\xymatrix@-1.75pc{
\overset{}{\bullet} & & \overset{}{\bullet} 
& &\ldots & & 
\overset{}{\bullet} & & \overset{}{\bullet}
& & \overset{}{\bullet} & &\overset{}{\bullet} 
& &\ldots & &  
\overset{}{\bullet} & &\overset{}{\bullet}   \\ 
& \ar@{-}[ul] \overset{}{\bullet} \ar@{-}[ur] 
& & & & & & \ar@{-}[ul] \overset{}{\bullet} \ar@{-}[ur] 
& & & & \ar@{-}[ul] \overset{}{\bullet} \ar@{-}[ur]
& & & & & & 
\ar@{-}[ul] \overset{}{\bullet} \ar@{-}[ur] &   \\ 
&  & \ddots & & & & &  \vdots & &  & & 
\vdots & & & & & \rddots
& &  \\ 
&  & & \overset{}{\bullet}& & & & 
\overset{}{\bullet} 
& & & & \overset{}{\bullet}& & & & 
\overset{}{\bullet} 
& & &   \\ 
&  & & & &  \ar@{-}[ull]\overset{}{\bullet}\ar@{-}[urr] 
& & & & & & & & \ar@{-}[ull]\overset{}{\bullet} \ar@{-}[urr]
& & & & &  \\ 
&  & & & & & & & &  \ar@{-}[ullll] \overset{}{\bullet}
\ar@{-}[urrrr]
& & & & & & & & & \\  }
\] 

\end{document}
Sigur
  • 37,330