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Transactions of the American Mathematical Society
Transactions of the American Mathematical Society
ISSN 1088-6850(online) ISSN 0002-9947(print)

 

How to make a triangulation of $S^3$ polytopal


Author: Simon A. King
Translated by:
Journal: Trans. Amer. Math. Soc. 356 (2004), 4519-4542
MSC (2000): Primary 52B11, 57M25; Secondary 57M15, 05C10, 52B22
Published electronically: February 27, 2004
MathSciNet review: 2067132
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Abstract: We introduce a numerical isomorphism invariant $p(\mathcal{T})$ for any triangulation $\mathcal{T}$ of $S^3$. Although its definition is purely topological (inspired by the bridge number of knots), $p(\mathcal{T})$ reflects the geometric properties of $\mathcal{T}$. Specifically, if $\mathcal{T}$ is polytopal or shellable, then $p(\mathcal{T})$is ``small'' in the sense that we obtain a linear upper bound for $p(\mathcal{T})$ in the number $n=n(\mathcal{T})$ of tetrahedra of $\mathcal{T}$. Conversely, if $p(\mathcal{T})$ is ``small'', then $\mathcal{T}$is ``almost'' polytopal, since we show how to transform $\mathcal{T}$ into a polytopal triangulation by $O((p(\mathcal{T}))^2)$ local subdivisions. The minimal number of local subdivisions needed to transform $\mathcal{T}$ into a polytopal triangulation is at least $\frac{p(\mathcal{T})}{3n}-n-2$.

Using our previous results [The size of triangulations supporting a given link, Geometry & Topology 5 (2001), 369-398], we obtain a general upper bound for $p(\mathcal{T})$ exponential in $n^2$. We prove here by explicit constructions that there is no general subexponential upper bound for $p(\mathcal{T})$ in $n$. Thus, we obtain triangulations that are ``very far'' from being polytopal.

Our results yield a recognition algorithm for $S^3$ that is conceptually simpler, although somewhat slower, than the famous Rubinstein-Thompson algorithm.


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Additional Information

Simon A. King
Affiliation: Department of Mathematics, Darmstadt University of Technology, Schlossgartenstr. 7, 64289 Darmstadt, Germany
Email: king@mathematik.tu-darmstadt.de

DOI: http://dx.doi.org/10.1090/S0002-9947-04-03465-8
PII: S 0002-9947(04)03465-8
Keywords: Convex polytope, dual graph, spatial graph, polytopality, bridge number, recognition of the $3$--sphere
Received by editor(s): May 28, 2002
Received by editor(s) in revised form: July 1, 2003
Published electronically: February 27, 2004
Article copyright: © Copyright 2004 American Mathematical Society