13 research outputs found
Representing convex geometries by almost-circles
Finite convex geometries are combinatorial structures. It follows from a
recent result of M.\ Richter and L.G.\ Rogers that there is an infinite set
of planar convex polygons such that with respect to geometric
convex hulls is a locally convex geometry and every finite convex geometry can
be represented by restricting the structure of to a finite subset in a
natural way. An \emph{almost-circle of accuracy} is a
differentiable convex simple closed curve in the plane having an inscribed
circle of radius and a circumscribed circle of radius such that
the ratio is at least . % Motivated by Richter and
Rogers' result, we construct a set such that (1) contains
all points of the plane as degenerate singleton circles and all of its
non-singleton members are differentiable convex simple closed planar curves;
(2) with respect to the geometric convex hull operator is a locally
convex geometry; (3) as opposed to , is closed with respect
to non-degenerate affine transformations; and (4) for every (small) positive
and for every finite convex geometry, there are continuum
many pairwise affine-disjoint finite subsets of such that each
consists of almost-circles of accuracy and the convex geometry
in question is represented by restricting the convex hull operator to . The
affine-disjointness of and means that, in addition to , even is disjoint from for every
non-degenerate affine transformation .Comment: 18 pages, 6 figure
On implicational bases of closure systems with unique critical sets
We show that every optimum basis of a finite closure system, in D.Maier's
sense, is also right-side optimum, which is a parameter of a minimum CNF
representation of a Horn Boolean function. New parameters for the size of the
binary part are also established. We introduce a K-basis of a general closure
system, which is a refinement of the canonical basis of Duquenne and Guigues,
and discuss a polynomial algorithm to obtain it. We study closure systems with
the unique criticals and some of its subclasses, where the K-basis is unique. A
further refinement in the form of the E-basis is possible for closure systems
without D-cycles. There is a polynomial algorithm to recognize the D-relation
from a K-basis. Thus, closure systems without D-cycles can be effectively
recognized. While E-basis achieves an optimum in one of its parts, the
optimization of the others is an NP-complete problem.Comment: Presented on International Symposium of Artificial Intelligence and
Mathematics (ISAIM-2012), Ft. Lauderdale, FL, USA Results are included into
plenary talk on conference Universal Algebra and Lattice Theory, June 2012,
Szeged, Hungary 29 pages and 2 figure
Optimum basis of finite convex geometry
Convex geometries form a subclass of closure systems with unique
criticals, or UC-systems. We show that the F-basis introduced in [6] for UC-
systems, becomes optimum in convex geometries, in two essential parts of the
basis: right sides (conclusions) of binary implications and left sides (premises)
of non-binary ones. The right sides of non-binary implications can also be
optimized, when the convex geometry either satis es the Carousel property,
or does not have D-cycles. The latter generalizes a result of P.L. Hammer
and A. Kogan for acyclic Horn Boolean functions. Convex geometries of order
convex subsets in a poset also have tractable optimum basis. The problem of
tractability of optimum basis in convex geometries in general remains to be
ope
Optimum basis of finite convex geometry
Convex geometries form a subclass of closure systems with unique
criticals, or UC-systems. We show that the F-basis introduced in [6] for UC-
systems, becomes optimum in convex geometries, in two essential parts of the
basis: right sides (conclusions) of binary implications and left sides (premises)
of non-binary ones. The right sides of non-binary implications can also be
optimized, when the convex geometry either satis es the Carousel property,
or does not have D-cycles. The latter generalizes a result of P.L. Hammer
and A. Kogan for acyclic Horn Boolean functions. Convex geometries of order
convex subsets in a poset also have tractable optimum basis. The problem of
tractability of optimum basis in convex geometries in general remains to be
ope
Connecting Political Communication with Urban Politics: A Bourdieusian Framework
In this article, I connect political communication with urban politics by conceptualizing an interdisciplinary urban politics research framework. Drawing on Pierre Bourdieu’s theories of practice and communication, I offer an urban politics research model that simultaneously addresses the dimensions of power struggle and symbolic struggle in urban politics. The theoretical modeling is discussed from an interdisciplinary approach to social studies and constructed with a methodological suggestion of tripartite social network analysis
On the complexity of enumerating pseudo-intents
AbstractWe investigate whether the pseudo-intents of a given formal context can efficiently be enumerated. We show that they cannot be enumerated in a specified lexicographic order with polynomial delay unless P=NP. Furthermore we show that if the restriction on the order of enumeration is removed, then the problem becomes at least as hard as enumerating minimal transversals of a given hypergraph. We introduce the notion of minimal pseudo-intents and show that recognizing minimal pseudo-intents is polynomial. Despite their less complicated nature, surprisingly it turns out that minimal pseudo-intents cannot be enumerated in output-polynomial time unless P=NP
On implicational bases of closure system with unique critical sets
We show that every optimum basis of a nite closure system,
in D. Maier's sense, is also right-side optimum, which is a parameter of a
minimum CNF representation of a Horn Boolean function. New parameters
for the size of the binary part are also established. We introduce the K-basis
of a general closure system, which is a re nement of the canonical basis of
V. Duquenne and J.L. Guigues, and discuss a polynomial algorithm to obtain
it. We study closure systems with unique critical sets, and some subclasses
of these where the K-basis is unique. A further re nement in the form of the
E-basis is possible for closure systems without D-cycles. There is a polynomial
algorithm to recognize the D-relation from a K-basis. Thus, closure systems
without D-cycles can be e ectively recognized. While the E-basis achieves an
optimum in one of its parts, the optimization of the others is an NP-complete
proble
On implicational bases of closure system with unique critical sets
We show that every optimum basis of a nite closure system,
in D. Maier's sense, is also right-side optimum, which is a parameter of a
minimum CNF representation of a Horn Boolean function. New parameters
for the size of the binary part are also established. We introduce the K-basis
of a general closure system, which is a re nement of the canonical basis of
V. Duquenne and J.L. Guigues, and discuss a polynomial algorithm to obtain
it. We study closure systems with unique critical sets, and some subclasses
of these where the K-basis is unique. A further re nement in the form of the
E-basis is possible for closure systems without D-cycles. There is a polynomial
algorithm to recognize the D-relation from a K-basis. Thus, closure systems
without D-cycles can be e ectively recognized. While the E-basis achieves an
optimum in one of its parts, the optimization of the others is an NP-complete
proble