10,249 research outputs found
Universal service financing in competitive postal markets : one size does not fill all
In the postal sector, the net cost of universal service depends on the content of the service, the postal market characteristics and the country’s geographical configuration. These three groups of factors affect both the direct cost of providing the service and the extent of competition on the market. In this paper, we consider countries with different geographical characteristics and we show that the choice of an appropriate mechanism to share the cost of universal service between market participants depends on the country configuration. Thus, for universal service financing, one size does not fit all.universal service obligations, compensation fund, market liberalization, cream- skimming
Irreversible Investment under L\'evy Uncertainty: an Equation for the Optimal Boundary
We derive a new equation for the optimal investment boundary of a general
irreversible investment problem under exponential L\'evy uncertainty. The
problem is set as an infinite time-horizon, two-dimensional degenerate singular
stochastic control problem. In line with the results recently obtained in a
diffusive setting, we show that the optimal boundary is intimately linked to
the unique optional solution of an appropriate Bank-El Karoui representation
problem. Such a relation and the Wiener Hopf factorization allow us to derive
an integral equation for the optimal investment boundary. In case the
underlying L\'evy process hits any real point with positive probability we show
that the integral equation for the investment boundary is uniquely satisfied by
the unique solution of another equation which is easier to handle. As a
remarkable by-product we prove the continuity of the optimal investment
boundary. The paper is concluded with explicit results for profit functions of
(i) Cobb-Douglas type and (ii) CES type. In the first case the function is
separable and in the second case non-separable.Comment: 19 page
Change-point model on nonhomogeneous Poisson processes with application in copy number profiling by next-generation DNA sequencing
We propose a flexible change-point model for inhomogeneous Poisson Processes,
which arise naturally from next-generation DNA sequencing, and derive score and
generalized likelihood statistics for shifts in intensity functions. We
construct a modified Bayesian information criterion (mBIC) to guide model
selection, and point-wise approximate Bayesian confidence intervals for
assessing the confidence in the segmentation. The model is applied to DNA Copy
Number profiling with sequencing data and evaluated on simulated spike-in and
real data sets.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS517 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Polygon Exploration with Time-Discrete Vision
With the advent of autonomous robots with two- and three-dimensional scanning
capabilities, classical visibility-based exploration methods from computational
geometry have gained in practical importance. However, real-life laser scanning
of useful accuracy does not allow the robot to scan continuously while in
motion; instead, it has to stop each time it surveys its environment. This
requirement was studied by Fekete, Klein and Nuechter for the subproblem of
looking around a corner, but until now has not been considered in an online
setting for whole polygonal regions.
We give the first algorithmic results for this important algorithmic problem
that combines stationary art gallery-type aspects with watchman-type issues in
an online scenario: We demonstrate that even for orthoconvex polygons, a
competitive strategy can be achieved only for limited aspect ratio A (the ratio
of the maximum and minimum edge length of the polygon), i.e., for a given lower
bound on the size of an edge; we give a matching upper bound by providing an
O(log A)-competitive strategy for simple rectilinear polygons, using the
assumption that each edge of the polygon has to be fully visible from some scan
point.Comment: 28 pages, 17 figures, 2 photographs, 3 tables, Latex. Updated some
details (title, figures and text) for final journal revision, including
explicit assumption of full edge visibilit
Reverse Nearest Neighbor Heat Maps: A Tool for Influence Exploration
We study the problem of constructing a reverse nearest neighbor (RNN) heat
map by finding the RNN set of every point in a two-dimensional space. Based on
the RNN set of a point, we obtain a quantitative influence (i.e., heat) for the
point. The heat map provides a global view on the influence distribution in the
space, and hence supports exploratory analyses in many applications such as
marketing and resource management. To construct such a heat map, we first
reduce it to a problem called Region Coloring (RC), which divides the space
into disjoint regions within which all the points have the same RNN set. We
then propose a novel algorithm named CREST that efficiently solves the RC
problem by labeling each region with the heat value of its containing points.
In CREST, we propose innovative techniques to avoid processing expensive RNN
queries and greatly reduce the number of region labeling operations. We perform
detailed analyses on the complexity of CREST and lower bounds of the RC
problem, and prove that CREST is asymptotically optimal in the worst case.
Extensive experiments with both real and synthetic data sets demonstrate that
CREST outperforms alternative algorithms by several orders of magnitude.Comment: Accepted to appear in ICDE 201
General Bounds for Incremental Maximization
We propose a theoretical framework to capture incremental solutions to
cardinality constrained maximization problems. The defining characteristic of
our framework is that the cardinality/support of the solution is bounded by a
value that grows over time, and we allow the solution to be
extended one element at a time. We investigate the best-possible competitive
ratio of such an incremental solution, i.e., the worst ratio over all
between the incremental solution after steps and an optimum solution of
cardinality . We define a large class of problems that contains many
important cardinality constrained maximization problems like maximum matching,
knapsack, and packing/covering problems. We provide a general
-competitive incremental algorithm for this class of problems, and show
that no algorithm can have competitive ratio below in general.
In the second part of the paper, we focus on the inherently incremental
greedy algorithm that increases the objective value as much as possible in each
step. This algorithm is known to be -competitive for submodular objective
functions, but it has unbounded competitive ratio for the class of incremental
problems mentioned above. We define a relaxed submodularity condition for the
objective function, capturing problems like maximum (weighted) (-)matching
and a variant of the maximum flow problem. We show that the greedy algorithm
has competitive ratio (exactly) for the class of problems that satisfy
this relaxed submodularity condition.
Note that our upper bounds on the competitive ratios translate to
approximation ratios for the underlying cardinality constrained problems.Comment: fixed typo
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