160 research outputs found
Bipartite regular graphs and shortness parameters
By constructing sequences of non-Hamiltonian graphs it is proved that (1) for k ⩾ 4, the class of k-connected k-valent bipartite graphs has shortness exponent less than one and (2) the class of cyclically 4-edge-connected trivalent bipartite graphs has shortness coefficient less than one
Hamiltonicity in multitriangular graphs
The family of 5-valent polyhedral graphs whose faces are all triangles or 3s-gons, s ≥ 9, is shown to contain non-hamiltonian graphs and to have a shortness exponent smaller than one
Shaken dynamics: an easy way to parallel MCMC
We define a Markovian parallel dynamics for a class of spin systems on
general interaction graphs. In this dynamics, beside the usual set of
parameters , the strength of the interaction between the spins
and , and , the external field at site ,
there is an inertial parameter measuring the tendency of the system to
remain locally in the same state. This dynamics is reversible with an
explicitly defined stationary measure. For suitable choices of parameter this
invariant measure concentrates on the ground states of the Hamiltonian. This
implies that this dynamics can be used to solve, heuristically, difficult
problems in the context of combinatorial optimization. We also study the
dynamics on with homogeneous interaction and external field and
with arbitrary boundary conditions. We prove that for certain values of the
parameters the stationary measure is close to the related Gibbs measure. Hence
our dynamics may be a good tool to sample from Gibbs measure by means of a
parallel algorithm. Moreover we show how the parameter allow to interpolate
between spin systems defined on different regular lattices.Comment: 5 figure
Embedding of Complete Graphs in Broken Chimera Graphs
In order to solve real world combinatorial optimization problems with a
D-Wave quantum annealer it is necessary to embed the problem at hand into the
D-Wave hardware graph, namely Chimera or Pegasus. Most hard real world problems
exhibit a strong connectivity. For the worst case scenario of a complete graph,
there exists an efficient solution for the embedding into the ideal Chimera
graph. However, since real machines almost always have broken qubits it is
necessary to find an embedding into the broken hardware graph.
We present a new approach to the problem of embedding complete graphs into
broken Chimera graphs. This problem can be formulated as an optimization
problem, more precisely as a matching problem with additional linear
constraints. Although being NP-hard in general it is fixed parameter tractable
in the number of inaccessible vertices in the Chimera graph. We tested our
exact approach on various instances of broken hardware graphs, both related to
real hardware as well as randomly generated. For fixed runtime, we were able to
embed larger complete graphs compared to previous, heuristic approaches. As an
extension, we developed a fast heuristic algorithm which enables us to solve
even larger instances. We compared the performance of our heuristic and exact
approaches.Comment: 26 pages, 9 figures, 2 table
Zero temperature solutions of the Edwards-Anderson model in random Husimi Lattices
We solve the Edwards-Anderson model (EA) in different Husimi lattices. We
show that, at T=0, the structure of the solution space depends on the parity of
the loop sizes. Husimi lattices with odd loop sizes have always a trivial
paramagnetic solution stable under 1RSB perturbations while, in Husimi lattices
with even loop sizes, this solution is absent. The range of stability under
1RSB perturbations of this and other RS solutions is computed analytically
(when possible) or numerically. We compute the free-energy, the complexity and
the ground state energy of different Husimi lattices at the level of the 1RSB
approximation. We also show, when the fraction of ferromagnetic couplings
increases, the existence, first, of a discontinuous transition from a
paramagnetic to a spin glass phase and latter of a continuous transition from a
spin glass to a ferromagnetic phase.Comment: 20 pages, 10 figures (v3: Corrected analysis of transitions. Appendix
proof fixed
Connectivity and Cycles in Graphs
https://digitalcommons.memphis.edu/speccoll-faudreerj/1199/thumbnail.jp
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