Abstract
Convex geometry is a closure space \((G,\phi )\) with the anti-exchange property. A classical result of Edelman and Jamison (1985) claims that every finite convex geometry is a join of several linear sub-geometries, and the smallest number of such sub-geometries necessary for representation is called the convex dimension. In our work we find necessary and sufficient conditions on a closure operator \(\phi \) of convex geometry \((G,\phi )\) so that its convex dimension equals 2, equivalently, they are represented by segments on a line. These conditions, for a given convex geometry \((G,\phi )\), can be checked in polynomial time in two parameters: the size of the base set |G| and the size of the implicational basis of \((G,\phi )\).
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Acknowledgements
We are grateful to Hofstra University that provided funds for both authors to travel to the conference Algebras and Lattices in Hawai’i-2018, where the results of this paper were presented. We want to thank Madina Bolat (University of Illinois in Urbana-Champaign), for her valuable comments and the help in producing the pictures. Other comments were sent by Gabor Czédli, Michael Richter and Jean-Paul Doignon. Many improvements in the paper were done thanks to a careful review, and we would like to thank our reviewers.
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Dedicated to Ralph Freese, Bill Lampe, and J.B. Nation.
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This article is part of the topical collection “Algebras and Lattices in Hawaii” edited by W. DeMeo.
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Adaricheva, K., Gjonbalaj, G. Description of closure operators in convex geometries of segments on the line. Algebra Univers. 80, 44 (2019). https://doi.org/10.1007/s00012-019-0620-6
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DOI: https://doi.org/10.1007/s00012-019-0620-6
Keywords
- Closure system
- Convex geometry
- Anti-exchange property
- Affine convex geometry
- Implicational basis
- Convex dimension
- Extreme points
- Carathéodory condition
- Convex geometry of circles
- Convex geometry of segments