simple graph vertex coloring
cGraph = SW_FSUB(conn, nExt)
It creates a simple graph vertex coloring, determines non connected
sublattices for Monte-Carlo calculation.
Input:
conn Contains edge indices which are connected
conn(1,idx)-->conn(2,idx), dimensions are [2 nConn].
nExt Size of the magnetic unit cell in units of cells.
Output:
cGraph Vector, that assigns every magnetic moment to a sublattice.
See also SW.ANNEAL.