doi:10.1016/j.dam.2007.08.012
Copyright © 2007 Elsevier B.V. All rights reserved.
Expected rank and randomness in rooted graphs
aDepartment of Computer Science Princeton University, 35 Olden Street, Princeton, NJ 08540, USA
bDepartment of Biostatistics, Johns Hopkins University, Baltimore, MD 21205, USA
cDepartment of Mathematics, 301 Thackeray Hall University of Pittsburgh, Pittsburgh, PA 15260, USA
dDepartment of Mathematics, Lafayette College, Easton, PA 18042, USA
eDepartment of Mathematics, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA
Received 24 July 2006;
revised 14 May 2007;
accepted 12 August 2007.
Available online 10 October 2007.
Abstract
For a rooted graph G, let EVb(G;p) be the expected number of vertices reachable from the root when each edge has an independent probability p of operating successfully. We determine the expected value of EVb(G;p) for random trees, and include a connection to unrooted trees. We also consider rooted digraphs, computing the expected value of a random orientation of a rooted graph G in terms of EVb(G;p). We consider optimal location of the root vertex for the class of grid graphs, and we also briefly discuss a polynomial that incorporates vertex failure.
Keywords: Expected rank; Probabilistic graph
Fig. 1. The six pre-ordered labeled trees on four vertices.
Fig. 3. The possible orientations of C3.
Fig. 4. The grid G5,6 with edges in A in bold.
This work was supported by NSF grant DMS-0243763.