xypic: How to typeset the dashed line in this diagram?

Question

I use xypics for diagrams, but I don't know how to put the dashed line in the diagram below. Search didn't find much. Can anybody here help?

Answer 1

Here's a way to do it without putting an extra column into the diagram. The dashed line is again inserted as a dashed arrow with no head or tail, i.e., \ar@{--}, but we'll specify both the source and the target of the arrow. In addition, both the source and the target of the arrow will be displaced from one of the nodes. The actual specification of the dashed line is

\ar@{--}[]+<3.5em,0em>;[dddd]+<3.5em,0em>

Note the semicolon; that means that the source is the thing before it and the target is the thing after it. The source is thus []+<3.5em,0em>. Since [] denotes the current node, the source is the point 3.5em to the right and 0em down from the current node.

Similarly, the target of the arrow is [dddd]+<3.5em,0em>, which means the point 3.5em to the right and 0em down from the node [dddd].

Here's a complete latex file:

\documentclass{article}
\usepackage[cmtip,all]{xy}
\begin{document}
\thispagestyle{empty}
\begin{displaymath}
  \xymatrix  {
    && 0\ar[d] \ar@{--}[]+<3.5em,0em>;[dddd]+<3.5em,0em>
    & 0\ar[d]
    &  0\ar[d]\\
    & 0\ar[d] \ar[r]
    & \Gamma^n\Omega^1 \ar[d] \ar[r]^-{d}
    & \Gamma^{n-1}\Omega^1\otimes\Omega^1\ar[d] \ar[r]^{d}
    & \Gamma^{n-2}\Omega^1\otimes\Omega^2 \ar[d] \ar[r]
    & \cdots   \\
    0 \ar[r]
    & A\ar[d]_{Id} \ar[r]^{d^1}
    & P^n\ar[d] \ar[r]^-{D}
    & P^{n-1}\otimes \Omega^1\ar[d] \ar[r]^{D}
    & P^{n-2}\otimes \Omega^2\ar[d] \ar[r] & \cdots \\ 
    0 \ar[r]
    & A\ar[d]_{Id} \ar[r]^{d^1}
    & P^{n-1}\ar[d] \ar[r]^-{D}
    & P^{n-2}\otimes \Omega^1\ar[d] \ar[r]^{D}
    & P^{n-3}\otimes \Omega^2\ar[d] \ar[r]
    & \cdots \\  
    & 0
    & 0
    & 0
    & 0
  }
\end{displaymath}
\end{document}

It produces

Answer 2

I believe that the only possibility is to insert a new column from the first line to the last one, without entries.

You can control the space between columns changing the value 2em.

Probably it is not possible to change the space only for some columns.

\[ 
\xymatrix@C=2em@R=2em{ &  & 0\ar[d] & \ar@{--}[dddd] & 0\ar[d] &  0\ar[d] &  &  \\ & 0\ar[d] \ar[r]  & \Gamma^n\Omega^1 \ar[d] \ar[rr]^{d} && \Gamma^{n-1}\Omega^1\otimes\Omega^1\ar[d] \ar[r]^{d}& \Gamma^{n-2}\Omega^1\otimes\Omega^2 \ar[d] \ar[r]& \cdots   \\  0 \ar[r] & A\ar[d]_{Id} \ar[r]^{d^1} & P^n\ar[d] \ar[rr]^{D} && P^{n-1}\otimes \Omega^1\ar[d] \ar[r]^{D} & P^{n-2}\otimes \Omega^2\ar[d] \ar[r] & \cdots \\ 
 0 \ar[r] & A\ar[d]_{Id} \ar[r]^{d^1} & P^{n-1}\ar[d] \ar[rr]^{D} && P^{n-2}\otimes \Omega^1\ar[d] \ar[r]^{D} & P^{n-3}\otimes \Omega^2\ar[d] \ar[r] & \cdots \\  
 & 0 & 0 && 0 & 0 &  
  }  \]