  The organizational structure of a network is investigated with a simulated
precipitation model which does not make use of prior knowledge about the
community structure of the network. The result is presented as a structure
profile through which various definitions of communities can be applied for
specific applications. The simulated precipitation model performs the grouping
of nodes so that nodes belonging to the same 'community' automatically
aggregate, thereby revealing regions of the adjacency matrix with denser
interconnections. The process is analogous to massive particles precipitating
towards the lower potential layer. Without loss of the infrastructure
information, a community structure profile of a network can be obtained as the
ground state of the Hamiltonian. The method is also applicable to directed and
weighted networks.
