4,848 research outputs found
More indecomposable polyhedra
We apply combinatorial methods to a geometric problem: the classification of
polytopes, in terms of Minkowski decomposability. Various properties of
skeletons of polytopes are exhibited, each sufficient to guarantee
indecomposability of a significant class of polytopes. We illustrate further
the power of these techniques, compared with the traditional method of
examining triangular faces, with several applications. In any dimension , we show that of all the polytopes with or fewer edges,
only one is decomposable. In 3 dimensions, we complete the classification, in
terms of decomposability, of the 260 combinatorial types of polyhedra with 15
or fewer edges.Comment: PDFLaTeX, 21 pages, 6 figure
Algebraic vertices of non-convex polyhedra
In this article we define an algebraic vertex of a generalized polyhedron and
show that it is the smallest set of points needed to define the polyhedron. We
prove that the indicator function of a generalized polytope is a linear
combination of indicator functions of simplices whose vertices are algebraic
vertices of . We also show that the indicator function of any generalized
polyhedron is a linear combination, with integer coefficients, of indicator
functions of cones with apices at algebraic vertices and line-cones. The
concept of an algebraic vertex is closely related to the Fourier--Laplace
transform. We show that a point is an algebraic vertex of a
generalized polyhedron if and only if the tangent cone of , at
, has non-zero Fourier--Laplace transform.Comment: 13 pages, 3 figure
Computational Geometry Column 42
A compendium of thirty previously published open problems in computational
geometry is presented.Comment: 7 pages; 72 reference
Rolling of Coxeter polyhedra along mirrors
The topic of the paper are developments of -dimensional Coxeter polyhedra.
We show that the surface of such polyhedron admits a canonical cutting such
that each piece can be covered by a Coxeter -dimensional domain.Comment: 20pages, 15 figure
On Monotone Sequences of Directed Flips, Triangulations of Polyhedra, and Structural Properties of a Directed Flip Graph
This paper studied the geometric and combinatorial aspects of the classical
Lawson's flip algorithm in 1972. Let A be a finite set of points in R2, omega
be a height function which lifts the vertices of A into R3. Every flip in
triangulations of A can be associated with a direction. We first established a
relatively obvious relation between monotone sequences of directed flips
between triangulations of A and triangulations of the lifted point set of A in
R3. We then studied the structural properties of a directed flip graph (a
poset) on the set of all triangulations of A. We proved several general
properties of this poset which clearly explain when Lawson's algorithm works
and why it may fail in general. We further characterised the triangulations
which cause failure of Lawson's algorithm, and showed that they must contain
redundant interior vertices which are not removable by directed flips. A
special case if this result in 3d has been shown by B.Joe in 1989. As an
application, we described a simple algorithm to triangulate a special class of
3d non-convex polyhedra. We proved sufficient conditions for the termination of
this algorithm and show that it runs in O(n3) time.Comment: 40 pages, 35 figure
The Parma Polyhedra Library: Toward a Complete Set of Numerical Abstractions for the Analysis and Verification of Hardware and Software Systems
Since its inception as a student project in 2001, initially just for the
handling (as the name implies) of convex polyhedra, the Parma Polyhedra Library
has been continuously improved and extended by joining scrupulous research on
the theoretical foundations of (possibly non-convex) numerical abstractions to
a total adherence to the best available practices in software development. Even
though it is still not fully mature and functionally complete, the Parma
Polyhedra Library already offers a combination of functionality, reliability,
usability and performance that is not matched by similar, freely available
libraries. In this paper, we present the main features of the current version
of the library, emphasizing those that distinguish it from other similar
libraries and those that are important for applications in the field of
analysis and verification of hardware and software systems.Comment: 38 pages, 2 figures, 3 listings, 3 table
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