  A flow approach to community detection in complex network and multilayer
network systems is proposed. Two methods have been developed to search for
communities in a network system (NS). The first of them is based on the
calculation of flow influence parameters of NS's subsystems, selected according
to the principle of nesting hierarchy. The second method uses the concept of
flow core of network system. Two methods are also proposed for community
detection in multilayer network system (MLNS). The first of them is based on
the concept of MLNS aggregate-network and subsequent allocation of its flow
core. The second method uses the concept of flow core of the process of
intersystem interactions in general. All developed methods are based on the use
of flow criterion that the selected group of nodes really forms a community.
The results of application of developed approaches are illustrated by examples
for which known methods are ineffective.
