244,266 research outputs found
Quadtrees as an Abstract Domain
Quadtrees have proved popular in computer graphics and spatial databases as a way of representing regions in two dimensional space. This hierarchical data-structure is flexible enough to support non-convex and even disconnected regions, therefore it is natural to ask whether this datastructure can form the basis of an abstract domain. This paper explores this question and suggests that quadtrees offer a new approach to weakly relational domains whilst their hierarchical structure naturally lends itself to representation with boolean functions
Benchmarks for Parity Games (extended version)
We propose a benchmark suite for parity games that includes all benchmarks
that have been used in the literature, and make it available online. We give an
overview of the parity games, including a description of how they have been
generated. We also describe structural properties of parity games, and using
these properties we show that our benchmarks are representative. With this work
we provide a starting point for further experimentation with parity games.Comment: The corresponding tool and benchmarks are available from
https://github.com/jkeiren/paritygame-generator. This is an extended version
of the paper that has been accepted for FSEN 201
Demography in a new key
The widespread opinion that demography is lacking in theory is based in part on a particular view of the nature of scientific theory, generally known as logical empiricism [or positivism]. A newer school of philosophy of science, the model-based view, provides a different perspective on demography, one that enhances its status as a scientific discipline. From this perspective, much of formal demography can be seen as a collection of substantive models of population dynamics [how populations and cohorts behave], in short, theoretical knowledge. And many theories in behavioural demography - often discarded as too old or too simplistic - can be seen as perfectly good scientific theory, useful for many purposes, although often in need of more rigorous statement.demographic models, demographic theory, methodology, philosophy of science, population theory, the structure of demographic knowledge
Tumbling of polymers in semidilute solution under shear flow
The tumbling dynamics of individual polymers in semidilute solution is
studied by large-scale non-equilibrium mesoscale hydrodynamic simulations. We
find that the tumbling time is equal to the non-equilibrium relaxation time of
the polymer end-to-end distance along the flow direction and strongly depends
on concentration. In addition, the normalized tumbling frequency as well as the
widths of the alignment distribution functions for a given
concentration-dependent Weissenberg number exhibit a weak concentration
dependence in the cross-over regime from a dilute to a semidilute solution. For
semidilute solutions a universal behavior is obtained. This is a consequence of
screening of hydrodynamic interactions at polymer concentrations exceeding the
overlap concentration
Stable Marriage with Ties and Bounded Length Preference Lists
We consider variants of the classical stable marriage problem in which preference lists may contain ties, and may be of bounded length. Such restrictions arise naturally in practical applications, such as centralised matching schemes that assign graduating medical students to their first hospital posts. In such a setting, weak stability is the most common solution concept, and it is known that weakly stable matchings can have different sizes. This motivates the problem of finding a maximum cardinality weakly stable matching, which is known to be NP-hard in general. We show that this problem is solvable in polynomial time if each man's list is of length at most 2 (even for women's lists that are of unbounded length). However if each man's list is of length at most 3, we show that the problem becomes NP-hard and not approximable within some d > 1, even if each woman's list is of length at most 4
- …