ISSN:
1432-0444
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Informatik
,
Mathematik
Notizen:
Abstract. Neighborly cubical polytopes exist: for any n≥ d≥ 2r+2 , there is a cubical convex d -polytope C d n whose r -skeleton is combinatorially equivalent to that of the n -dimensional cube. This solves a problem of Babson, Billera, and Chan. Kalai conjectured that the boundary $\partial C_d^n$ of a neighborly cubical polytope C d n maximizes the f -vector among all cubical (d-1) -spheres with 2 n vertices. While we show that this is true for polytopal spheres if n≤ d+1 , we also give a counterexample for d=4 and n=6 . Further, the existence of neighborly cubical polytopes shows that the graph of the n -dimensional cube, where n\ge5 , is ``dimensionally ambiguous'' in the sense of Grünbaum. We also show that the graph of the 5 -cube is ``strongly 4 -ambiguous.'' In the special case d=4 , neighborly cubical polytopes have f 3 =(f 0 /4) log 2 (f 0 /4) vertices, so the facet—vertex ratio f 3 /f 0 is not bounded; this solves a problem of Kalai, Perles, and Stanley studied by Jockusch.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/s004540010039
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