the distance-sum-connectivity matrix of g. Will be
automatically calculated if not supplied.
Value
ID number (WID) and the self-returning ID number (SID). The former is
based on the sum of all walks weighted according to vertex distance
degrees. The latter is limited to self-returning walks.
References
K. Szymanski, W. Mueller, J. Knop, and N. Trinajsti\'c.
On the Identification Numbers for Chemical Structures.
International Journal of Quantum Chemistry, 30(S20):173-183, 1986