I have a cluster with which the objects are simply bullets. I would like to group some of the bullets such as the following.

Somehow the edges of the box are exactly on the bullets. Here is my code

   $\xymatrix@C=1cm@R=1cm{ *={\bullet}\ar@{-}[r]&*={\bullet}\ar@{-}[r]&*={\bullet}\ar@{-}[r]\ar@{-}[d]&*={\bullet} \save "1,1"."2,3"*[F.]\frm{}\\ *={\bullet}\ar@{-}[r]&*={\bullet}\ar@{-}[r]&*={\bullet}\ar@{-}[r]&*={\bullet} \restore}%$


which resulting the following image.

I just need to insert paddings within the box. Or if anybody know another way to draw this with xymatrix would also be great.

You can use

\save "1,1"."2,3"*+<1pc>!<.5pc,-.5pc>\frm{.}


which having saved the positions increases the size of the rectangle by 1pc in the bottom and right directions and then moves it .5pc vertically and horizontally to be centered on the original material. You do not need the extra [F.] command, the \frm{.} is sufficient.

\documentclass{article}

\usepackage[all]{xy}

\begin{document}
$\xymatrix@C=1cm@R=1cm@M=1pc{ *={\bullet}\ar@{-}[r]&*={\bullet}\ar@{-}[r]&*={\bullet}\ar@{-}[r]\ar@{-}[d] &*={\bullet} \save "1,1"."2,3"*+<1pc>!<.5pc,-.5pc>\frm{.}\\ *={\bullet}\ar@{-}[r]&*={\bullet}\ar@{-}[r]&*={\bullet}\ar@{-}[r] &*={\bullet} \restore}%$

\end{document}


Using tikz....

\documentclass{article}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\foreach \y in {0,2}
{
\foreach \x in {0,2,4,6}  \fill (\x,\y) circle(1mm);
\draw[very thick] (0,\y)--(6,\y);
}
\draw[very thick](4,0)--(4,2);
\draw[densely dotted, very thick] (-0.2,-0.2) rectangle (4.2,2.2);
\end{tikzpicture}
\end{document}

• Thanks! It works but I was waiting for the xy-pic version. – Cica Gustiani Feb 14 '17 at 22:31
• Don't know anything about xy-pic, but it looks torturous. – JPi Feb 14 '17 at 23:42
• somehow recently I've been working with this xy-pic and get used to a bit with the notation. I have no particular reason why this package instead – Cica Gustiani Feb 15 '17 at 9:18