10,925 research outputs found
Robust Fault Tolerant uncapacitated facility location
In the uncapacitated facility location problem, given a graph, a set of
demands and opening costs, it is required to find a set of facilities R, so as
to minimize the sum of the cost of opening the facilities in R and the cost of
assigning all node demands to open facilities. This paper concerns the robust
fault-tolerant version of the uncapacitated facility location problem (RFTFL).
In this problem, one or more facilities might fail, and each demand should be
supplied by the closest open facility that did not fail. It is required to find
a set of facilities R, so as to minimize the sum of the cost of opening the
facilities in R and the cost of assigning all node demands to open facilities
that did not fail, after the failure of up to \alpha facilities. We present a
polynomial time algorithm that yields a 6.5-approximation for this problem with
at most one failure and a 1.5 + 7.5\alpha-approximation for the problem with at
most \alpha > 1 failures. We also show that the RFTFL problem is NP-hard even
on trees, and even in the case of a single failure
Fault Tolerant Clustering Revisited
In discrete k-center and k-median clustering, we are given a set of points P
in a metric space M, and the task is to output a set C \subseteq ? P, |C| = k,
such that the cost of clustering P using C is as small as possible. For
k-center, the cost is the furthest a point has to travel to its nearest center,
whereas for k-median, the cost is the sum of all point to nearest center
distances. In the fault-tolerant versions of these problems, we are given an
additional parameter 1 ?\leq \ell \leq ? k, such that when computing the cost
of clustering, points are assigned to their \ell-th nearest-neighbor in C,
instead of their nearest neighbor. We provide constant factor approximation
algorithms for these problems that are both conceptually simple and highly
practical from an implementation stand-point
Designing application software in wide area network settings
Progress in methodologies for developing robust local area network software has not been matched by similar results for wide area settings. The design of application software spanning multiple local area environments is examined. For important classes of applications, simple design techniques are presented that yield fault tolerant wide area programs. An implementation of these techniques as a set of tools for use within the ISIS system is described
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