Adding labels to graph in xy package

Question

I'm using xy package to draw a simple graph representation. How can I add the labels to the egdes?

Here is the code I've produced so far:

\xygraph{
!{<0cm,0cm>;<1cm,0cm>:<0cm,1cm>::}
!{(0,1) }*+{\bullet_{r}}="r"
!{(3,0) }*+{\bullet_{k1}}="k1"
!{(4,1) }*+{\bullet_{a}}="a"
!{(2,1) }*+{\bullet_{b}}="b"
!{(3,2) }*+{\bullet_{c}}="c"
!{(2,3) }*+{\bullet_{d}}="d"
!{(1,2) }*+{\bullet_{e}}="e"
"k1":"a" "k1":"b"
"b":"c" "a":"c"
"b":"r"
"c":"d" "d":"e"
"e":"b"
}

Answer 1

For the record:

There are a few possibilities to add labels to edges.

• "a":"b"^{e_1} adds the label above the edge (above as when going from a to b)
• "a":"b"_{e_1} adds the label below the edge
• "a":"b"|{e_1} adds the label on the edge

When placing a label on the edge itself, it makes sense to do it like "a":"b"|*+{e_1}, as this ensures the edge is broken and the text easily readable.

You could also change the position of the label using "a":"b"^(0.2){e_1}, which places the label 20 % into the edge. This works with all three ways.

It is amazing what you can do using xypic once you begin to understand it - which I am far away from...