Helly numbers of algebraic subsets of ℝd and an extension of Doignon’s Theorem
-
J. A. De Loera
,
R. N. La Haye
Abstract
We study S-convex sets, which are the geometric objects obtained as the intersection of the usual convex sets in ℝd with a proper subset S ⊂ ℝd, and contribute new results about their S-Helly numbers. We extend prior work for S = ℝd, ℤd, and ℤd−k × ℝk, and give some sharp bounds for several new cases: low-dimensional situations, sets that have some algebraic structure, in particular when S is an arbitrary subgroup of ℝd or when S is the difference between a lattice and some of its sublattices. By abstracting the ingredients of Lovász method we obtain colorful versions of many monochromatic Helly-type results, including several colorful versions of our own results.
Acknowledgements
We are grateful to Andrés De Loera-Brust for his suggestions on computing the Helly number of ℙ2. This research was supported by a UC MEXUS grant that helped to establish the collaboration of the UC Davis and UNAM teams. We are grateful for the support.
Funding
The first, second and third authors’ travel was supported in part by the Institute for Mathematics and its Applications and an NSA grant. The third and fourth authors were also supported by CONACYT project 166306 and PAPIIT IN104915.
References
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© 2017 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Frontmatter
- Ricci solitons on four-dimensional Lorentzian Walker manifolds
- The exterior splash in PG(6, q): carrier conics
- Central figure-8 cross-cuts make surfaces cylindrical
- Vieta’s formulae for regular polynomials of a quaternionic variable
- On characterizations of sausages via inequalities and roots of Steiner polynomials
- On maximal symplectic partial spreads
- Helly numbers of algebraic subsets of ℝd and an extension of Doignon’s Theorem
- A maximum problem of S.-T. Yau for variational p-capacity
- Drapeable unit arcs fit in the unit 30° sector
- Uniform Lie algebras and uniformly colored graphs
- A Krasnosel’skii-type theorem for an enlarged class of orthogonal polytopes
Articles in the same Issue
- Frontmatter
- Ricci solitons on four-dimensional Lorentzian Walker manifolds
- The exterior splash in PG(6, q): carrier conics
- Central figure-8 cross-cuts make surfaces cylindrical
- Vieta’s formulae for regular polynomials of a quaternionic variable
- On characterizations of sausages via inequalities and roots of Steiner polynomials
- On maximal symplectic partial spreads
- Helly numbers of algebraic subsets of ℝd and an extension of Doignon’s Theorem
- A maximum problem of S.-T. Yau for variational p-capacity
- Drapeable unit arcs fit in the unit 30° sector
- Uniform Lie algebras and uniformly colored graphs
- A Krasnosel’skii-type theorem for an enlarged class of orthogonal polytopes
