Showing papers on "Regular polygon published in 2010"

Generalized Gaussian quadrature rules on arbitrary polygons

Abstract: In this paper, we present a numerical algorithm based on group theory and numerical optimization to compute efficient quadrature rules for integration of bivariate polynomials over arbitrary polygons. These quadratures have desirable properties such as positivity of weights and interiority of nodes and can readily be used as software libraries where numerical integration within planar polygons is required. We have used this algorithm for the construction of symmetric and non-symmetric quadrature rules over convex and concave polygons. While in the case of symmetric quadratures our results are comparable to available rules, the proposed algorithm has the advantage of being flexible enough so that it can be applied to arbitrary planar regions for the integration of generalized classes of functions. To demonstrate the efficiency of the new quadrature rules, we have tested them for the integration of rational polygonal shape functions over a regular hexagon. For a relative error of 10−8 in the computation of stiffness matrix entries, one needs at least 198 evaluation points when the region is partitioned, whereas 85 points suffice with our quadrature rule. Copyright © 2009 John Wiley & Sons, Ltd.

The Pentagram Map: A Discrete Integrable System

Abstract: The pentagram map is a projectively natural transformation defined on (twisted) polygons. A twisted polygon is a map from \({\mathbb Z}\) into \({{\mathbb{RP}}^2}\) that is periodic modulo a projective transformation called the monodromy. We find a Poisson structure on the space of twisted polygons and show that the pentagram map relative to this Poisson structure is completely integrable. For certain families of twisted polygons, such as those we call universally convex, we translate the integrability into a statement about the quasi-periodic motion for the dynamics of the pentagram map. We also explain how the pentagram map, in the continuous limit, corresponds to the classical Boussinesq equation. The Poisson structure we attach to the pentagram map is a discrete version of the first Poisson structure associated with the Boussinesq equation. A research announcement of this work appeared in [16].

Random Convex Hulls and Extreme Value Statistics

Abstract: In this paper we study the statistical properties of convex hulls of N random points in a plane chosen according to a given distribution. The points may be chosen independently or they may be correlated. After a non-exhaustive survey of the somewhat sporadic literature and diverse methods used in the random convex hull problem, we present a unifying approach, based on the notion of support function of a closed curve and the associated Cauchy’s formulae, that allows us to compute exactly the mean perimeter and the mean area enclosed by the convex polygon both in case of independent as well as correlated points. Our method demonstrates a beautiful link between the random convex hull problem and the subject of extreme value statistics. As an example of correlated points, we study here in detail the case when the points represent the vertices of n independent random walks. In the continuum time limit this reduces to n independent planar Brownian trajectories for which we compute exactly, for all n, the mean perimeter and the mean area of their global convex hull. Our results have relevant applications in ecology in estimating the home range of a herd of animals. Some of these results were announced recently in a short communication [Phys. Rev. Lett. 103:140602, 2009].

Constructing Extended Formulations from Reflection Relations

Abstract: There are many examples of optimization problems whose associated polyhedra can be described much nicer, and with way less inequalities, by projections of higher dimensional polyhedra than this would be possible in the original space. However, currently not many general tools to construct such extended formulations are available. In this paper, we develop a framework of polyhedral relations that generalizes inductive constructions of extended formulations via projections, and we particularly elaborate on the special case of reflection relations. The latter ones provide polynomial size extended formulations for several polytopes that can be constructed as convex hulls of the unions of (exponentially) many copies of an input polytope obtained via sequences of reflections at hyperplanes. We demonstrate the use of the framework by deriving small extended formulations for the G-permutahedra of all finite reflection groups G (generalizing both Goeman's extended formulation of the permutahedron of size O(n log n) and Ben-Tal and Nemirovski's extended formulation with O(k) inequalities for the regular 2^k-gon) and for Huffman-polytopes (the convex hulls of the weight-vectors of Huffman codes).

Simulated annealing applied to the irregular rotational placement of shapes over containers with fixed dimensions

Abstract: This work deals with the problem of minimizing the waste of space that occurs on a rotational placement of a set of irregular two dimensional polygons inside a two dimensional container. This problem is approached with an heuristic based on simulated annealing. Traditional ''external penalization'' techniques are avoided through the application of the no-fit polygon, that determinates the collision free area for each polygon before its placement. The simulated annealing controls: the rotation applied, the placement and the sequence of placement of the polygons. For each non placed polygon, a limited depth binary search is performed to find a scale factor that when applied to the polygon, would allow it to be fitted in the container. It is proposed a crystallization heuristic, in order to increase the number of accepted solutions. The bottom left and larger first deterministic heuristics were also studied. The proposed process is suited for non convex polygons and containers, the containers can have holes inside.

The linking number and the writhe of uniform random walks and polygons in confined spaces

Abstract: Random walks and polygons are used to model polymers. In this paper we consider the extension of the writhe, self-linking number and linking number to open chains. We then study the average writhe, self-linking and linking number of random walks and polygons over the space of configurations as a function of their length. We show that the mean squared linking number, the mean squared writhe and the mean squared self-linking number of oriented uniform random walks or polygons of length n, in a convex confined space, are of the form O(n2). Moreover, for a fixed simple closed curve in a convex confined space, we prove that the mean absolute value of the linking number between this curve and a uniform random walk or polygon of n edges is of the form . Our numerical studies confirm those results. They also indicate that the mean absolute linking number between any two oriented uniform random walks or polygons, of n edges each, is of the form O(n). Equilateral random walks and polygons are used to model polymers in θ-conditions. We use numerical simulations to investigate how the self-linking and linking number of equilateral random walks scale with their length.

Research on the coverage path planning of UAVs for polygon areas

Abstract: This paper proposes an improved method of exact cellular decomposition to plan the coverage path in polygon area. Firstly, the problem of Coverage Path Planning (CPP) in the convex polygon area is transformed to the width calculation of the convex polygon, and the strategy of flying along the vertical direction of width is presented to reach the least number of turns. Secondly, a convex decomposition algorithm of minimum width sum based on the greedy recursive method is presented to decompose the concave area into some convex subregions. Finally, a subregion connection algorithm based on minimum traversal of undirected graph is proposed to connect the coverage paths of the subregions. The simulation shows that the proposed method is feasible and effective.

Accelerating regular polygon beams.

Abstract: Beams that possess high-intensity peaks that follow curved paths of propagation under linear diffraction have recently been shown to have a multitude of interesting uses. In this Letter, a family of phase-only masks is derived, and each mask gives rise to multiple accelerating intensity maxima. The curved paths of the peaks can be described by the vertices of a regular polygon that is centered on the optic axis and expands with propagation.

Polygonal Homographic Orbits of the Curved n-Body Problem

Abstract: In the $2$-dimensional $n$-body problem, $n\ge 3$, in spaces of constant curvature, $\kappa e 0$, we study polygonal homographic solutions. We first provide necessary and sufficient conditions for the existence of these orbits and then consider the case of regular polygons. We further use this criterion to show that, for any $n\ge 3$, the regular $n$-gon is a polygonal homographic orbit if and only if all masses are equal. Then we prove the existence of relative equilibria of non-equal masses on the sphere of curvature $\kappa>0$ for $n=3$ in the case of scalene triangles. Such triangular relative equilibria occur only along fixed geodesics and are generated from fixed points of the sphere. Finally, through a classification of the isosceles case, we prove that not any three masses can form a triangular relative equilibrium.

Implant system having at least three support elements

Abstract: The invention relates to an implant system that comprises a concave spherical-segment-shaped socket part (2) and a corresponding convex spherical-segment-shaped joint part (1). The joint part (1) rests in the socket part (2), wherein according to the invention, at least three support elements (3) that describe a spherical triangle or a spherical polygon are arranged on the surface of the joint part (1) or on the surface of the socket part (2).

Inradius and Circumradius of Various Convex Cones Arising in Applications

Abstract: This note addresses the issue of computing the inradius and the circumradius of a convex cone in a Euclidean space. It deals also with the related problem of finding the incenter and the circumcenter of the cone. We work out various examples of convex cones arising in applications.

On the injectivity of Wachspress and mean value mappings between convex polygons

Abstract: Wachspress and mean value coordinates are two generalizations of triangular barycentric coordinates to convex polygons and have recently been used to construct mappings between polygons, with application to curve deformation and image warping. We show that Wachspress mappings between convex polygons are always injective but that mean value mappings can fail to be so in extreme cases.

The Direct Kinematics of Objects Suspended From Cables

Abstract: This work addresses the problem for determining the position and orientation of an object with regular polygon suspended from n cables with the same length when the n robots form a regular polygon on the horizontal plane. First, an analytic algorithm based on resultant elimination is presented to determine all possible equilibrium configurations of the planar 4-bar linkage. As the nonlinear system can be reduced to a polynomial equation in one unknown with a degree 8, this algorithm is more efficient than numerical search algorithms. Then, considering that the motion of the 3D cable system in its vertical planes of symmetry can be regarded as the motion of an equivalent planar 4-bar linkage, the proposed algorithm is used to solve the direct kinematic problem of objects suspended from multiple cables. Then, case studies with three to six cables are conducted for demonstration. Finally, experiments are conducted for validation.© 2010 ASME

Spectral method on quadrilaterals

Abstract: In this paper, we investigate the spectral method on quadrilaterals. We introduce an orthogonal family of functions induced by Legendre polynomials, and establish some results on the corresponding orthogonal approximation. These results play important roles in the spectral method for partial differential equations defined on quadrilaterals. As examples of applications, we provide spectral schemes for two model problems and prove their spectral accuracy in Jacobi weighted Sobolev space. Numerical results coincide well with the analysis. We also investigate the spectral method on convex polygons whose solutions possess spectral accuracy. The approximation results of this paper are also applicable to other problems.

Approximate Shortest Path Algorithms for Sequences of Pairwise Disjoint Simple Polygons

Abstract: Assume that two points p and q are given and a finite ordered set of simple polygons, all in the same plane; the basic version of a touring-a-sequence-of-polygons problem (TPP) is to find a shortest path such that it starts at p, then visits these polygons in the given order, and ends at q. This paper describes four approximation algorithms for unconstrained versions of problems defined by touring an ordered set of polygons. It contributes to an approximate and partial answer to the previously open problem “What is the complexity of the touringpolygons problem for pairwise disjoint, simple and not necessarily convex polygons?” by providing (")O(n) approximation algorithms for solving this problem, either for given start and end points p and q, or with allowing to have those variable, where n is the total number of vertices of the given k simple and pairwise disjoint polygons; (") defines the numerical accuracy in dependency of a selected " > 0.

Grasping Non-stretchable Cloth Polygons

Abstract: In this paper, we examine non-stretchable two-dimensional polygonal cloth, and place bounds on the number of fingers needed to immobilize it. For any non-stretchable cloth polygon, it is always necessary to pin all of the convex vertices. We show that for some shapes, more fingers are necessary. No more than one-third of the concave vertices need to be pinned for simple polygons, and no more than one-third of the concave vertices plus two fingers per hole are necessary for polygons with holes.

Discriminant coamoebas in dimension two

Abstract: This paper deals with coamoebas, that is, images under coordinatewise argument mappings, of certain quite particular plane algebraic curves. These curves are the zero sets of reduced A-discriminants of two variables. We consider the coamoeba primarily as a subset of the torus T^2=(R/2\pi Z)^2, but also as a subset of its covering space R^2, in which case the coamoeba consists of an infinite, doubly periodic image. In fact, it turns out to be natural to take multiplicities into account, and thus to treat the coamoeba as a chain in the sense of algebraic topology. We give a very explicit description of the coamoeba as the union of two mirror images of a (generally non-convex) polygon, which is easily constructed from a matrix B that represents the Gale transform of the original collection A. We also give an area formula for the coamoeba, and we show that the coamoeba is intimately related to a certain zonotope. In fact, on the torus T^2 the coamoeba and the zonotope together form a cycle, and hence precisely cover the entire torus an integer number of times. This integer is proved to be equal to the (normalized) volume of the convex hull of A.

Exact moduli space metrics for hyperbolic vortex polygons

Abstract: Exact metrics on some totally geodesic submanifolds of the moduli space of static hyperbolic N-vortices are derived. These submanifolds, denoted as Σn,m, are spaces of Cn-invariant vortex configurations with n single vortices at the vertices of a regular polygon and m=N−n coincident vortices at the polygon’s center. The geometric properties of Σn,m are investigated, and it is found that Σn,n−1 is isometric to the hyperbolic plane of curvature −(3πn)−1. The geodesic flow on Σn,m and a geometrically natural variant of geodesic flow recently proposed by Collie and Tong [“The dynamics of Chern-Simons vortices,” Phys. Rev. D Part. Fields Gravit. Cosmol. 78, 065013 (2008);e-print arXiv:hep-th/0805.0602] are analyzed in detail.

Second-order properties and central limit theory for the vertex process of iteration infinitely divisible and iteration stable random tessellations in the plane

Abstract: The point process of vertices of an iteration infinitely divisible or, more specifically, of an iteration stable random tessellation in the Euclidean plane is considered. We explicitly determine its covariance measure and its pair-correlation function, as well as the cross-covariance measure and the cross-correlation function of the vertex point process and the random length measure in the general nonstationary regime. We also give special formulae in the stationary and isotropic setting. Exact formulae are given for vertex count variances in compact and convex sampling windows, and asymptotic relations are derived. Our results are then compared with those for a Poisson line tessellation having the same length density parameter. Moreover, a functional central limit theorem for the joint process of suitably rescaled total edge counts and edge lengths is established with the process (ξ, tξ), t > 0, arising in the limit, where ξ is a centered Gaussian variable with explicitly known variance.

Total curvature and simple pursuit on domains of curvature bounded above

Abstract: We show how circumradius and asymptotic behavior of curves in cat(0) and cat(K) spaces (K > 0) are controlled by growth rates of total curvature. We apply our results to pursuit and evasion games of capture type with simple pursuit motion, generalizing results that are known for convex Euclidean domains, and obtaining results that are new for convex Euclidean domains and hold on playing fields vastly more general than these.

Optimal polygonal representation of planar graphs

Abstract: In this paper, we consider the problem of representing graphs by polygons whose sides touch. We show that at least six sides per polygon are necessary by constructing a class of planar graphs that cannot be represented by pentagons. We also show that the lower bound of six sides is matched by an upper bound of six sides with a linear time algorithm for representing any planar graph by touching hexagons. Moreover, our algorithm produces convex polygons with edges with slopes 0, 1, -1.

Drawing area-proportional Venn-3 diagrams with convex polygons

Abstract: Area-proportional Venn diagrams are a popular way of visualizing the relationships between data sets, where the set intersections have a specified numerical value. In these diagrams, the areas of the regions are in proportion to the given values. Venn-3, the Venn diagram consisting of three intersecting curves, has been used in many applications, including marketing, ecology and medicine. Whilst circles are widely used to draw such diagrams, most area specifications cannot be drawn in this way and, so, should only be used where an approximate solution is acceptable. However, placing different restrictions on the shape of curves may result in usable diagrams that have an exact solution, that is, where the areas of the regions are exactly in proportion to the represented data. In this paper, we explore the use of convex shapes for drawing exact area proportional Venn-3 diagrams. Convex curves reduce the visual complexity of the diagram and, as most desirable shapes (such as circles, ovals and rectangles) are convex, the work described here may lead to further drawing methods with these shapes. We describe methods for constructing convex diagrams with polygons that have four or five sides and derive results concerning which area specifications can be drawn with them. This work improves the state-of-the-art by extending the set of area specifications that can be drawn in a convex manner. We also show how, when a specification cannot be drawn in a convex manner, a non-convex drawing can be generated.

Drawing Graphs in the Plane with a Prescribed Outer Face and Polynomial Area

Abstract: We study the classic graph drawing problem of drawing a planar graph using straight-line edges with a prescribed convex polygon as the outer face. Unlike previous algorithms for this problem, which may produce drawings with exponential area, our method produces drawings with polynomial area. In addition, we allow for collinear points on the boundary, provided such vertices do not create overlapping edges. Thus, we solve an open problem of Duncan et al., which, when combined with their work, implies that we can produce a planar straight-line drawing of a combinatorially-embedded genus-g graph with the graph's canonical polygonal schema drawn as a convex polygonal external face.

Viviani's Theorem and Its Extension

Abstract: SummaryViviani's theorem states that the sum of distances from any point inside an equilateral triangle to its sides is constant Here, in an extension of this result, we show, using linear program

Sharpness of Falconer's estimate in continuous and arithmetic settings, geometric incidence theorems and distribution of lattice points in convex domains

Abstract: In this paper we prove, for all $d \ge 2$, that for no $s<\frac{d+1}{2}$ does $I_s(\mu)<\infty$ imply the canonical Falconer distance problem incidence bound, or the analogous estimate where the Euclidean norm is replaced by the norm generated by a particular convex body $B$ with a smooth boundary and everywhere non-vanishing curvature. Our construction, based on a combinatorial construction due to Pavel Valtr naturally leads us to some interesting connections between the problem under consideration, geometric incidence theorem in the discrete setting and distribution of lattice points in convex domains. We also prove that an example by Mattila can be discretized to produce a set of points and annuli for which the number of incidences is much greater than in the case of the lattice. In particular, we use the known results on the Gauss Circle Problem and a discretized version of Mattila's example to produce a non-lattice set of points and annuli where the number of incidences is much greater than in the case of the standard lattice. Finally, we extend Valtr's example into the setting of vector spaces over finite fields and show that a finite field analog of the key incidence bound is also sharp.