Abstract
A well-known consequence of John’s theorem states that any symmetric convex body K ⊂ ℝn in John’s position can be approximated by a polytope P with a polynomial number of facets in n, so that \(P\; \subset \;K\; \subset \;\sqrt n P\). This results extends to the non-symmetric case if the homothety ratio grows to n. In this note, we study how well this result holds in the non-symmetric case, if the homothety ratio is reduced below n. We prove the following: For R = o(n) and a sufficiently large n, there exists a convex body K ⊂ ℝn in John’s position for which there is no polytope P with a polynomial in n number of facets, such that K ⊂ P ⊂ RK. Moreover, for \(R = O\left({\sqrt n} \right)\), there exists a convex body for which a polytope with an exponential number of facets is needed.
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Acknowledgement
I am grateful to my Advisor, Mark Rudelson, for fruitful discussions. I am also grateful to the anonymous reviewer for his/her suggestions.
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Huang, H. John’s position is not good for approximation. Isr. J. Math. 234, 37–53 (2019). https://doi.org/10.1007/s11856-019-1924-0
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DOI: https://doi.org/10.1007/s11856-019-1924-0