103,355 research outputs found
Approximating Minimum Cost Connectivity Orientation and Augmentation
We investigate problems addressing combined connectivity augmentation and
orientations settings. We give a polynomial-time 6-approximation algorithm for
finding a minimum cost subgraph of an undirected graph that admits an
orientation covering a nonnegative crossing -supermodular demand function,
as defined by Frank. An important example is -edge-connectivity, a
common generalization of global and rooted edge-connectivity.
Our algorithm is based on a non-standard application of the iterative
rounding method. We observe that the standard linear program with cut
constraints is not amenable and use an alternative linear program with
partition and co-partition constraints instead. The proof requires a new type
of uncrossing technique on partitions and co-partitions.
We also consider the problem setting when the cost of an edge can be
different for the two possible orientations. The problem becomes substantially
more difficult already for the simpler requirement of -edge-connectivity.
Khanna, Naor, and Shepherd showed that the integrality gap of the natural
linear program is at most when and conjectured that it is constant
for all fixed . We disprove this conjecture by showing an
integrality gap even when
Confidentiality-Preserving Publish/Subscribe: A Survey
Publish/subscribe (pub/sub) is an attractive communication paradigm for
large-scale distributed applications running across multiple administrative
domains. Pub/sub allows event-based information dissemination based on
constraints on the nature of the data rather than on pre-established
communication channels. It is a natural fit for deployment in untrusted
environments such as public clouds linking applications across multiple sites.
However, pub/sub in untrusted environments lead to major confidentiality
concerns stemming from the content-centric nature of the communications. This
survey classifies and analyzes different approaches to confidentiality
preservation for pub/sub, from applications of trust and access control models
to novel encryption techniques. It provides an overview of the current
challenges posed by confidentiality concerns and points to future research
directions in this promising field
The Stochastic Reach-Avoid Problem and Set Characterization for Diffusions
In this article we approach a class of stochastic reachability problems with
state constraints from an optimal control perspective. Preceding approaches to
solving these reachability problems are either confined to the deterministic
setting or address almost-sure stochastic requirements. In contrast, we propose
a methodology to tackle problems with less stringent requirements than almost
sure. To this end, we first establish a connection between two distinct
stochastic reach-avoid problems and three classes of stochastic optimal control
problems involving discontinuous payoff functions. Subsequently, we focus on
solutions of one of the classes of stochastic optimal control problems---the
exit-time problem, which solves both the two reach-avoid problems mentioned
above. We then derive a weak version of a dynamic programming principle (DPP)
for the corresponding value function; in this direction our contribution
compared to the existing literature is to develop techniques that admit
discontinuous payoff functions. Moreover, based on our DPP, we provide an
alternative characterization of the value function as a solution of a partial
differential equation in the sense of discontinuous viscosity solutions, along
with boundary conditions both in Dirichlet and viscosity senses. Theoretical
justifications are also discussed to pave the way for deployment of
off-the-shelf PDE solvers for numerical computations. Finally, we validate the
performance of the proposed framework on the stochastic Zermelo navigation
problem
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