5,633 research outputs found
Approximating Upper Degree-Constrained Partial Orientations
In the Upper Degree-Constrained Partial Orientation problem we are given an
undirected graph , together with two degree constraint functions
. The goal is to orient as many edges as possible,
in such a way that for each vertex the number of arcs entering is
at most , whereas the number of arcs leaving is at most .
This problem was introduced by Gabow [SODA'06], who proved it to be MAXSNP-hard
(and thus APX-hard). In the same paper Gabow presented an LP-based iterative
rounding -approximation algorithm.
Since the problem in question is a special case of the classic 3-Dimensional
Matching, which in turn is a special case of the -Set Packing problem, it is
reasonable to ask whether recent improvements in approximation algorithms for
the latter two problems [Cygan, FOCS'13; Sviridenko & Ward, ICALP'13] allow for
an improved approximation for Upper Degree-Constrained Partial Orientation. We
follow this line of reasoning and present a polynomial-time local search
algorithm with approximation ratio . Our algorithm uses a
combination of two types of rules: improving sets of bounded pathwidth from the
recent -approximation algorithm for 3-Set Packing [Cygan,
FOCS'13], and a simple rule tailor-made for the setting of partial
orientations. In particular, we exploit the fact that one can check in
polynomial time whether it is possible to orient all the edges of a given graph
[Gy\'arf\'as & Frank, Combinatorics'76].Comment: 12 pages, 1 figur
Constant Factor Approximation for Capacitated k-Center with Outliers
The -center problem is a classic facility location problem, where given an
edge-weighted graph one is to find a subset of vertices ,
such that each vertex in is "close" to some vertex in . The
approximation status of this basic problem is well understood, as a simple
2-approximation algorithm is known to be tight. Consequently different
extensions were studied.
In the capacitated version of the problem each vertex is assigned a capacity,
which is a strict upper bound on the number of clients a facility can serve,
when located at this vertex. A constant factor approximation for the
capacitated -center was obtained last year by Cygan, Hajiaghayi and Khuller
[FOCS'12], which was recently improved to a 9-approximation by An, Bhaskara and
Svensson [arXiv'13].
In a different generalization of the problem some clients (denoted as
outliers) may be disregarded. Here we are additionally given an integer and
the goal is to serve exactly clients, which the algorithm is free to
choose. In 2001 Charikar et al. [SODA'01] presented a 3-approximation for the
-center problem with outliers.
In this paper we consider a common generalization of the two extensions
previously studied separately, i.e. we work with the capacitated -center
with outliers. We present the first constant factor approximation algorithm
with approximation ratio of 25 even for the case of non-uniform hard
capacities.Comment: 15 pages, 3 figures, accepted to STACS 201
Valuation and Hedging of Contracts with Funding Costs and Collateralization
The research presented in this work is motivated by recent papers by Brigo et
al. (2011), Burgard and Kjaer (2009), Cr\'epey (2012), Fujii and Takahashi
(2010), Piterbarg (2010) and Pallavicini et al. (2012). Our goal is to provide
a sound theoretical underpinning for some results presented in these papers by
developing a unified framework for the non-linear approach to hedging and
pricing of OTC financial contracts. We introduce a systematic approach to
valuation and hedging in nonlinear markets, that is, in markets where cash
flows of the financial contracts may depend on the hedging strategies. Our
systematic approach allows to identify primary sources of and quantify various
adjustment to valuation and hedging, primarily the funding and liquidity
adjustment and credit risk adjustment. We propose a way to define no-arbitrage
in such nonlinear markets, and we provide conditions that imply absence of
arbitrage in some specific market trading models. Accordingly, we formulate a
concept of no-arbitrage price, and we provide relevant (non-linear) BSDE that
produces the no-arbitrage price in case when the contract's cash flows can be
replicated
LOGISTIC MANAGEMENT IN COMMERCE ENTERPRISES
The importance of logistic management for the general developmentstrategy of functioning of the enterprise is a stimulus to consider it in terms of newmethodology in enterprise management. Taking into account the up-to-date experiencesof logistics, either as a scientific branch or a practice, logistic management cannot betreated in the same way as the system management, through its aims, or the strategicmanagement understood as new method of management.logistic, management, enterprises
Exact solutions for Big Bounce in loop quantum cosmology
In this paper we study the flat (k=0) cosmological FRW model with holonomy
corrections of Loop Quantum Gravity. The considered universe contains a
massless scalar field and the cosmological constant Lambda. We find analytical
solutions for this model in different configurations and investigate its
dynamical behaviour in the whole phase space. We show the explicit influence of
Lambda on the qualitative and quantitative character of solutions. Even in the
case of positive Lambda the oscillating solutions without the initial and final
singularity appear as a generic case for some quantisation schemes.Comment: 12 pages, 12 figures, added references and changed introduction and
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