14,629 research outputs found
A new approach to graph reconstruction using supercards
The vertex-deleted subgraph G - v, obtained from the graph G
by deleting the vertex v and all edges incident to v, is called a
card of G. The deck of G is the multiset of its unlabelled vertex-
deleted subgraphs. The number of common cards of G and H is
the cardinality of a maximum multiset of common cards, i.e., the
multiset intersection of the decks of G and H. We introduce a new
approach to the study of common cards using supercards, where
we define a supercard G+ of G and H to be a graph that has at
least one vertex-deleted subgraph isomorphic to G, and at least
one isomorphic to H. We show how maximum sets of common
cards of G and H correspond to certain sets of permutations of
the vertices of a supercard, which we call maximum saturating
sets. We then show how to construct supercards of various pairs
of graphs for which there exists some maximum saturating set X
contained in Aut(G+). For certain other pairs of graphs, we show
that it is possible to construct G+ and a maximum saturating set
X such that the elements of X that are not in Aut(G+) are in one-
to-one correspondence with a set of automorphisms of a different
supercard G+_lambda � of G and H. Our constructions cover nearly all of
the published families of pairs of graphs that have a large number
of common cards
Switching Reconstruction of Digraphs
Switching about a vertex in a digraph means to reverse the direction of every
edge incident with that vertex. Bondy and Mercier introduced the problem of
whether a digraph can be reconstructed up to isomorphism from the multiset of
isomorphism types of digraphs obtained by switching about each vertex. Since
the largest known non-reconstructible oriented graphs have 8 vertices, it is
natural to ask whether there are any larger non-reconstructible graphs. In this
paper we continue the investigation of this question. We find that there are
exactly 44 non-reconstructible oriented graphs whose underlying undirected
graphs have maximum degree at most 2. We also determine the full set of
switching-stable oriented graphs, which are those graphs for which all
switchings return a digraph isomorphic to the original
Size reconstructibility of graphs
The deck of a graph is given by the multiset of (unlabelled) subgraphs
. The subgraphs are referred to as the cards of .
Brown and Fenner recently showed that, for , the number of edges of a
graph can be computed from any deck missing 2 cards. We show that, for
sufficiently large , the number of edges can be computed from any deck
missing at most cards.Comment: 15 page
Isomorph-free generation of 2-connected graphs with applications
Many interesting graph families contain only 2-connected graphs, which have
ear decompositions. We develop a technique to generate families of unlabeled
2-connected graphs using ear augmentations and apply this technique to two
problems. In the first application, we search for uniquely K_r-saturated graphs
and find the list of uniquely K_4-saturated graphs on at most 12 vertices,
supporting current conjectures for this problem. In the second application, we
verifying the Edge Reconstruction Conjecture for all 2-connected graphs on at
most 12 vertices. This technique can be easily extended to more problems
concerning 2-connected graphs.Comment: 15 pages, 3 figures, 4 table
OS diversity for intrusion tolerance: Myth or reality?
One of the key benefits of using intrusion-tolerant systems is the possibility of ensuring correct behavior in the presence of attacks and intrusions. These security gains are directly dependent on the components exhibiting failure diversity. To what extent failure diversity is observed in practical deployment depends on how diverse are the components that constitute the system. In this paper we present a study with operating systems (OS) vulnerability data from the NIST National Vulnerability Database. We have analyzed the vulnerabilities of 11 different OSes over a period of roughly 15 years, to check how many of these vulnerabilities occur in more than one OS. We found this number to be low for several combinations of OSes. Hence, our analysis provides a strong indication that building a system with diverse OSes may be a useful technique to improve its intrusion tolerance capabilities
On rainbow tetrahedra in Cayley graphs
Let be the complete undirected Cayley graph of the odd cyclic
group . Connected graphs whose vertices are rainbow tetrahedra in
are studied, with any two such vertices adjacent if and only if they
share (as tetrahedra) precisely two distinct triangles. This yields graphs
of largest degree 6, asymptotic diameter and almost all vertices
with degree: {\bf(a)} 6 in ; {\bf(b)} 4 in exactly six connected subgraphs
of the -semi-regular tessellation; and {\bf(c)} 3 in exactly four
connected subgraphs of the -regular hexagonal tessellation. These
vertices have as closed neighborhoods the union (in a fixed way) of closed
neighborhoods in the ten respective resulting tessellations. Generalizing
asymptotic results are discussed as well.Comment: 21 pages, 7 figure
Cutoff for non-backtracking random walks on sparse random graphs
A finite ergodic Markov chain is said to exhibit cutoff if its distance to
stationarity remains close to 1 over a certain number of iterations and then
abruptly drops to near 0 on a much shorter time scale. Discovered in the
context of card shuffling (Aldous-Diaconis, 1986), this phenomenon is now
believed to be rather typical among fast mixing Markov chains. Yet,
establishing it rigorously often requires a challengingly detailed
understanding of the underlying chain. Here we consider non-backtracking random
walks on random graphs with a given degree sequence. Under a general sparsity
condition, we establish the cutoff phenomenon, determine its precise window,
and prove that the (suitably rescaled) cutoff profile approaches a remarkably
simple, universal shape
Recommended from our members
A computer system to perform structure comparison using TOPS representations of protein structure
We describe the design and implementation of a fast topology–based method
for protein structure comparison. The approach uses the TOPS topological representation
of protein structure, aligning two structures using a common discovered
pattern and generating measure of distance derived from an insert score. Heavy
use is made of a constraint-based pattern matching algorithm for TOPS diagrams
that we have designed and described elsewhere Gilbert et al. (1999). The comparison
system is maintained at the European Bioinformatics Institute and is available
over the Web via the at tops.ebi.ac.uk/tops. Users submit a structure description in
Protein Data Bank (PDB) format and can compare it with structures in the entire
PDB or a representative subset of protein domains, receiving the results by email
- …