Tuesday, 29 July 2008

gt.geometric topology - Simplicial and cubical decompositions of low valence

Every surface can be triangulated in such a way that at most 7 trianlges meet at one vertex. Every surface can be decomposed in squares such that at every vertex at most 5 suqares meet. For surfaces of genus more than 1 this is the low bound.



What happen in higher dimensions, for example for 3 and 4-manifolds, ect...? It should be easy to show that for every dimension $n$ there are numbers $S(n)$ and and $C(n)$ such that every manifold $M^n$ admits a simplicial decomposition with at most $S(n)$
simplexes at every vertex and a cubical decomposition with at most $C(n)$ cubes at every vertex. The refference of Gil below confirms this for $n=3$.



Here are three questions (I suspect they are hard).



1) Can it be proven that $C(n)>2^n$?



2) Can it be proven that $S(n)>frac{Vol(S^n)}{Vol(Delta^n)}$, where $Delta^n$ is the spherical tetrahedron with edge of length $frac{pi}{3}$ in the unit sphere $S^n$.



3) Is there any reasonable estimation for $C(n)$ and $S(n)$ from above?

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