112 research outputs found
Upper bounds for packings of spheres of several radii
We give theorems that can be used to upper bound the densities of packings of
different spherical caps in the unit sphere and of translates of different
convex bodies in Euclidean space. These theorems extend the linear programming
bounds for packings of spherical caps and of convex bodies through the use of
semidefinite programming. We perform explicit computations, obtaining new
bounds for packings of spherical caps of two different sizes and for binary
sphere packings. We also slightly improve bounds for the classical problem of
packing identical spheres.Comment: 31 page
An Inequality for Circle Packings Proved by SemidefiniteProgramming
A geometric inequality among three triangles, originating in circle packing problems, is introduced. In order to prove it, we reduce the original formulation to the nonnegativity of a polynomial in four real indeterminates. Techniques based on sum of squares decompositions, semidefinite programming and symmetry reduction are then applied to provide an easily verifiable nonnegativity certificat
Sphere packing bounds via spherical codes
The sphere packing problem asks for the greatest density of a packing of
congruent balls in Euclidean space. The current best upper bound in all
sufficiently high dimensions is due to Kabatiansky and Levenshtein in 1978. We
revisit their argument and improve their bound by a constant factor using a
simple geometric argument, and we extend the argument to packings in hyperbolic
space, for which it gives an exponential improvement over the previously known
bounds. Additionally, we show that the Cohn-Elkies linear programming bound is
always at least as strong as the Kabatiansky-Levenshtein bound; this result is
analogous to Rodemich's theorem in coding theory. Finally, we develop
hyperbolic linear programming bounds and prove the analogue of Rodemich's
theorem there as well.Comment: 30 pages, 2 figure
The Strong Dodecahedral Conjecture and Fejes Toth's Conjecture on Sphere Packings with Kissing Number Twelve
This article sketches the proofs of two theorems about sphere packings in
Euclidean 3-space. The first is K. Bezdek's strong dodecahedral conjecture: the
surface area of every bounded Voronoi cell in a packing of balls of radius 1 is
at least that of a regular dodecahedron of inradius 1. The second theorem is L.
Fejes Toth's contact conjecture, which asserts that in 3-space, any packing of
congruent balls such that each ball is touched by twelve others consists of
hexagonal layers. Both proofs are computer assisted. Complete proofs of these
theorems appear in the author's book "Dense Sphere Packings" and a related
preprintComment: The citations and title have been update
Packing ellipsoids with overlap
The problem of packing ellipsoids of different sizes and shapes into an
ellipsoidal container so as to minimize a measure of overlap between ellipsoids
is considered. A bilevel optimization formulation is given, together with an
algorithm for the general case and a simpler algorithm for the special case in
which all ellipsoids are in fact spheres. Convergence results are proved and
computational experience is described and illustrated. The motivating
application - chromosome organization in the human cell nucleus - is discussed
briefly, and some illustrative results are presented
The Gaussian core model in high dimensions
We prove lower bounds for energy in the Gaussian core model, in which point
particles interact via a Gaussian potential. Under the potential function with , we show that no point
configuration in of density can have energy less than
as with and
fixed. This lower bound asymptotically matches the upper bound of obtained as the expectation in the Siegel mean value
theorem, and it is attained by random lattices. The proof is based on the
linear programming bound, and it uses an interpolation construction analogous
to those used for the Beurling-Selberg extremal problem in analytic number
theory. In the other direction, we prove that the upper bound of is no longer asymptotically sharp when . As
a consequence of our results, we obtain bounds in for the
minimal energy under inverse power laws with , and
these bounds are sharp to within a constant factor as with
fixed.Comment: 30 pages, 1 figur
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