NewClusterGraph creates a new cluster graph with a dominant subsystem We assume the dominant is hard coded to be containment.

NewGraph creates a structure that holds one or more graphs.

NewSubsystem generates a new subsystem graph.

A ClusterGraph holds a single graph with one or more subsystems.

A graph holds one or more named clusters.

Metrics keeps track of counts of things.

A subsystem is a graph with a set of vertices that are connected by edges We use "vertex" instead of node to distinguish the graph vs.