# Curved arrow in xy-pic

\documentclass{article}
\usepackage{graphicx}
\usepackage[all]{xy}
\begin{document}
$\xymatrix{& A \ar[d] & B \ar[d] & C \ar[d] & \\ D \ar[r] & E \ar[d] \ar[r] & F \ar[r] \ar[d] & G \ar[d] \arr[d][l][llld][dddll][dddll] & \\ H \ar[r] & I \ar[d] \ar[r] & J \ar[r] \ar[d] & K \ar[r] \ar[d] & L \\ M \ar[r] & N \ar[d] \ar[r] & O \ar[d] \ar[r] & P \ar[r] \ar[d] & Q\\ & R & S & T &}$
\end{document}


The curved arrow:

{arr[d][l][llld][dddll][dddll]}


I'm using xy-pic to draw a commutative diagram with a curved arrow.

The code above gives the result in the picture, but I want a curved arrow like the blue one. I tried to adjust the code in the curved arrow but failed.

My question:

How can I draw the desired arrow using xy-pic?

An alternative method would be like this, but it will enlarge the whole diagram. And the relative coordinate is not valid for fractions.

Thanks for your time and effort!

• Please extend your sniplet to a full self contained minimal example that others can copy and play with as is. Here prople have to add their own preamble etc. That said, it is probably easier to do in tikz-cd instead of xy (I generally convert all \xymatrix diagrams to tikz-cd in the manuscripts I edit, IMO they look a lot better in tikz-cd) – daleif Jan 22 '20 at 10:40
• @daleif Thank you. I already fixed it. – Andrews Jan 22 '20 at 11:03

You need to double the number of columns, reducing the spacing between columns.

\documentclass{article}
\usepackage{amsmath}
\usepackage[all,cmtip]{xy}

\begin{document}

\begin{equation*}
\xymatrix@C=1pc{
&& A \ar[d] && B \ar[d] && C \ar[d] &&  \\
D \ar[rr] && E \ar[d] \ar[rr] && F \ar[d] \ar[rr] && G \ar[d]
\arr[d][ll][llllld][dddllll][dddllll]
&& \\
H \ar[rr] && I \ar[d] \ar[rr] && J \ar[d] \ar[rr] && K \ar[d] \ar[rr] && L \\
M \ar[rr] && N \ar[d] \ar[rr] && O \ar[d] \ar[rr] && P \ar[d] \ar[rr] && Q\\
&& R && S && T &&
}
\end{equation*}

\end{document}