e xpand
com pound graph
node s
contract clus te r
inclus ion e dge s
adjace ncy e dge s
Clus te r
Sim ple ve rte x
Inclus ion digraph
Adjace ncy graph
Prope rtie s
H ie rarch icalApproach
In
ν
O ut
dum m y
ve rtice s
In+ O ut:
m inim ize
cros s ings
Clus te r:
m inim ize
cros s ings
Clus te r
In+ O ut
no im prove m e nt
y-coordinate s
x-coordinate s