3,350 research outputs found
Connectivity Threshold for random subgraphs of the Hamming graph
We study the connectivity of random subgraphs of the -dimensional Hamming
graph , which is the Cartesian product of complete graphs on
vertices. We sample the random subgraph with an i.i.d.\ Bernoulli bond
percolation on with parameter . We identify the window of the
transition: when the probability that the graph is
connected goes to , while when it converges to
.
We also investigate the connectivity probability inside the critical window,
namely when .
We find that the threshold does not depend on , unlike the phase
transition of the giant connected component the Hamming graph (see [Bor et al,
2005]). Within the critical window, the connectivity probability does depend on
d. We determine how.Comment: 10 pages, no figure
Average Sensitivity of Graph Algorithms
In modern applications of graphs algorithms, where the graphs of interest are
large and dynamic, it is unrealistic to assume that an input representation
contains the full information of a graph being studied. Hence, it is desirable
to use algorithms that, even when only a (large) subgraph is available, output
solutions that are close to the solutions output when the whole graph is
available. We formalize this idea by introducing the notion of average
sensitivity of graph algorithms, which is the average earth mover's distance
between the output distributions of an algorithm on a graph and its subgraph
obtained by removing an edge, where the average is over the edges removed and
the distance between two outputs is the Hamming distance.
In this work, we initiate a systematic study of average sensitivity. After
deriving basic properties of average sensitivity such as composition, we
provide efficient approximation algorithms with low average sensitivities for
concrete graph problems, including the minimum spanning forest problem, the
global minimum cut problem, the minimum - cut problem, and the maximum
matching problem. In addition, we prove that the average sensitivity of our
global minimum cut algorithm is almost optimal, by showing a nearly matching
lower bound. We also show that every algorithm for the 2-coloring problem has
average sensitivity linear in the number of vertices. One of the main ideas
involved in designing our algorithms with low average sensitivity is the
following fact; if the presence of a vertex or an edge in the solution output
by an algorithm can be decided locally, then the algorithm has a low average
sensitivity, allowing us to reuse the analyses of known sublinear-time
algorithms and local computation algorithms (LCAs). Using this connection, we
show that every LCA for 2-coloring has linear query complexity, thereby
answering an open question.Comment: 39 pages, 1 figur
Long geodesics in subgraphs of the cube
A path in the hypercube is said to be a geodesic if no two of its edges
are in the same direction. Let be a subgraph of with average degree
. How long a geodesic must contain? We show that must contain a
geodesic of length . This result, which is best possible, strengthens a
theorem of Feder and Subi. It is also related to the `antipodal colourings'
conjecture of Norine.Comment: 8 page
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