17,979 research outputs found
Optimal Kullback-Leibler Aggregation via Information Bottleneck
In this paper, we present a method for reducing a regular, discrete-time
Markov chain (DTMC) to another DTMC with a given, typically much smaller number
of states. The cost of reduction is defined as the Kullback-Leibler divergence
rate between a projection of the original process through a partition function
and a DTMC on the correspondingly partitioned state space. Finding the reduced
model with minimal cost is computationally expensive, as it requires an
exhaustive search among all state space partitions, and an exact evaluation of
the reduction cost for each candidate partition. Our approach deals with the
latter problem by minimizing an upper bound on the reduction cost instead of
minimizing the exact cost; The proposed upper bound is easy to compute and it
is tight if the original chain is lumpable with respect to the partition. Then,
we express the problem in the form of information bottleneck optimization, and
propose using the agglomerative information bottleneck algorithm for searching
a sub-optimal partition greedily, rather than exhaustively. The theory is
illustrated with examples and one application scenario in the context of
modeling bio-molecular interactions.Comment: 13 pages, 4 figure
Bottleneck Surfaces and Worldsheet Geometry of Higher-Curvature Quantum Gravity
We describe a simple lattice model of higher-curvature quantum gravity in two
dimensions and study the phase structure of the theory as a function of the
curvature coupling. It is shown that the ensemble of flat graphs is
entropically unstable to the formation of baby universes. In these simplified
models the growth in graphs exhibits a branched polymer behaviour in the phase
directly before the flattening transition.Comment: 18 pages LaTeX, 3 .eps figures, uses epsf.tex; clarifying comments
added and typos correcte
Higher-Order Triangular-Distance Delaunay Graphs: Graph-Theoretical Properties
We consider an extension of the triangular-distance Delaunay graphs
(TD-Delaunay) on a set of points in the plane. In TD-Delaunay, the convex
distance is defined by a fixed-oriented equilateral triangle ,
and there is an edge between two points in if and only if there is an empty
homothet of having the two points on its boundary. We consider
higher-order triangular-distance Delaunay graphs, namely -TD, which contains
an edge between two points if the interior of the homothet of
having the two points on its boundary contains at most points of . We
consider the connectivity, Hamiltonicity and perfect-matching admissibility of
-TD. Finally we consider the problem of blocking the edges of -TD.Comment: 20 page
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