3,977 research outputs found
Approximating the generalized terminal backup problem via half-integral multiflow relaxation
We consider a network design problem called the generalized terminal backup
problem. Whereas earlier work investigated the edge-connectivity constraints
only, we consider both edge- and node-connectivity constraints for this
problem. A major contribution of this paper is the development of a strongly
polynomial-time 4/3-approximation algorithm for the problem. Specifically, we
show that a linear programming relaxation of the problem is half-integral, and
that the half-integral optimal solution can be rounded to a 4/3-approximate
solution. We also prove that the linear programming relaxation of the problem
with the edge-connectivity constraints is equivalent to minimizing the cost of
half-integral multiflows that satisfy flow demands given from terminals. This
observation presents a strongly polynomial-time algorithm for computing a
minimum cost half-integral multiflow under flow demand constraints
A simple dual ascent algorithm for the multilevel facility location problem
We present a simple dual ascent method for the multilevel facility location problem which finds a solution within times the optimum for the uncapacitated case and within times the optimum for the capacitated one. The algorithm is deterministic and based on the primal-dual technique. \u
LP-Based Algorithms for Capacitated Facility Location
Linear programming has played a key role in the study of algorithms for
combinatorial optimization problems. In the field of approximation algorithms,
this is well illustrated by the uncapacitated facility location problem. A
variety of algorithmic methodologies, such as LP-rounding and primal-dual
method, have been applied to and evolved from algorithms for this problem.
Unfortunately, this collection of powerful algorithmic techniques had not yet
been applicable to the more general capacitated facility location problem. In
fact, all of the known algorithms with good performance guarantees were based
on a single technique, local search, and no linear programming relaxation was
known to efficiently approximate the problem.
In this paper, we present a linear programming relaxation with constant
integrality gap for capacitated facility location. We demonstrate that the
fundamental theories of multi-commodity flows and matchings provide key
insights that lead to the strong relaxation. Our algorithmic proof of
integrality gap is obtained by finally accessing the rich toolbox of LP-based
methodologies: we present a constant factor approximation algorithm based on
LP-rounding.Comment: 25 pages, 6 figures; minor revision
Discrete Convex Functions on Graphs and Their Algorithmic Applications
The present article is an exposition of a theory of discrete convex functions
on certain graph structures, developed by the author in recent years. This
theory is a spin-off of discrete convex analysis by Murota, and is motivated by
combinatorial dualities in multiflow problems and the complexity classification
of facility location problems on graphs. We outline the theory and algorithmic
applications in combinatorial optimization problems
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