Network Node Order
The function returns an order of the nodes of a network that is compatible with its parent structure.
An order is compatible with the parent structure of a network if
each node has as parents only nodes appearing earlier in that order.
That such an order exists is guaranteed by the fact that every
catNetwork is a DAG (Directed Acyclic Graph). The result is one order out of, eventually, many possible.
a list of node indices.
N. Balov, P. Salzman