Neighboring nodes, returned as node indices if nodeID
is numeric, or as node names if nodeID is a node name. A
node that is connected to itself by an edge (a self-loop) is listed as its
own neighbor only once.
neighbors counts self-loops only once. In previous releases,
if node u had a self-loop, then neighbors(g,u)
listed u twice in the output. neighbors(g,u)
now returns only one instance of u.