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 זה הזמן לשינוי
 Combinatorics and More – Greatest Hits
 Ilan and me
 The Simplex, the Cyclic polytope, the Positroidron, the Amplituhedron, and Beyond
 From Oberwolfach: The Topological Tverberg Conjecture is False
 Midrasha Mathematicae #18: In And Around Combinatorics
 Quantum computing: achievable reality or unrealistic dream
 A Historical Picture Taken by Nimrod Megiddo
 Scott Triumphs* at the Shtetl
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 זה הזמן לשינוי
 Combinatorics and More  Greatest Hits
 The Simplex, the Cyclic polytope, the Positroidron, the Amplituhedron, and Beyond
 Believing that the Earth is Round When it Matters
 The Ultimate Riddle
 Academic Degrees and Sex
 Helly's Theorem, "Hypertrees", and Strange Enumeration I
 Answer: Lord Kelvin, The Age of the Earth, and the Age of the Sun
 The KadisonSinger Conjecture has beed Proved by Adam Marcus, Dan Spielman, and Nikhil Srivastava
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Category Archives: Convex polytopes
A Diameter Problem (6): Abstract Objective Functions
George Dantzig and Leonid Khachyan In this part we will not progress on the diameter problem that we discussed in the earlier posts but will rather describe a closely related problem for directed graphs associated with ordered families of sets. The role models for … Continue reading
Posted in Combinatorics, Convex polytopes, Open problems
Tagged Hirsch conjecture, Linear programming
7 Comments
A Diameter Problem (5)
6. First subexponential bounds. Proposition 1: How to prove it: This is easy to prove: Given two sets and in our family , we first find a path of the form where, and . We let with and consider the family … Continue reading
Diameter Problem (4)
Let us consider another strategy to deal with our diameter problem. Let us try to associate other graphs to our family of sets. Recall that we consider a family of subsets of size of the set . Let us now associate … Continue reading
Diameter Problem (3)
3. What we will do in this post and and in future posts We will now try all sorts of ideas to give good upper bounds for the abstract diameter problem that we described. As we explained, such bounds apply … Continue reading
Posted in Combinatorics, Convex polytopes, Open problems
Tagged Hirsch conjecture, Linear programming, Quasiautomated proofs
1 Comment
A Diameter Problem (2)
2. The connection with Hirsch’s Conjecture The Hirsch Conjecture asserts that the diameter of the graph G(P) of a dpolytope P with n facets is at most nd. Not even a polynomial upper bound for the diameter in terms of d and … Continue reading
Posted in Combinatorics, Convex polytopes, Open problems
5 Comments
A Diamater Problem for Families of Sets.
Let me draw your attention to the following problem: Consider a family of subsets of size d of the set N={1,2,…,n}. Associate to a graph as follows: The vertices of are simply the sets in . Two vertices and are adjacent … Continue reading
Posted in Combinatorics, Convex polytopes, Open problems
9 Comments
Euler’s Formula, Fibonacci, the BayerBillera Theorem, and Fine’s CDindex
Bill Gessley proving Euler’s formula (at UMKC) In the earlier post about Billerafest I mentioned the theorem of Bayer and Billera on flag numbers of polytopes. Let me say a little more about it. 1. Euler Euler’s theorem … Continue reading
Posted in Combinatorics, Convex polytopes
Tagged BayerBillera's theorem, CDindex, Flag numbers
3 Comments
Billerafest
I am unable to attend the conference taking place now at Cornell, but I send my warmest greetings to Lou from Jerusalem. The titles and abstracts of the lectures can be found here. Let me tell you about two theorems by Lou. … Continue reading
Posted in Conferences, Convex polytopes
Tagged fvectors, flag vectors, gconjecture, Lou Billera
1 Comment
Five Open Problems Regarding Convex Polytopes
The problems 1. The conjecture A centrally symmetric dpolytope has at least non empty faces. 2. The cubesimplex conjecture For every k there is f(k) so that every dpolytope with has a kdimensional face which is either a simplex … Continue reading