(click for poster)


As some of you might know, even Günter Ziegler does age. Indeed, he will turn 50 in 2013. Since he came to Berlin he had 22 graduate students (and counting!), he mentored 13+ postdocs, and 5+ people took their "Habilitation" with him.

These are more than enough reasons to CELEBRATE, and we intend to do so on

Saturday, May 25 2013

with a 1-day conference in Günter's honor. Lunch will be provided on site. The conference is followed by a dinner (BBQ) to which the whole family (former students, postdocs, collaborators, friends) are cordially invited to join; see registration for details.


9:00Registration opens
9:30Gil Kalai (Jerusalem, Yale). Geometric combinatorics, graphs and hypergraphs
I will describe how several questions in geometric combinatorics translate into questions about graphs and hypergraphs and back. Examples include:
  1. Borsuk's problem.
  2. Tverberg theorem and Tverberg type problems. Tverberg's theorem asserts that (r-1)(d+1)+1 points in d-space can be divided into r parts whose convex hull intersect. I will discuss situations where less points admit such a partition and connections with graph theory.
  3. Helly type theorems and conditions on induced subgraphs and sub-hypergraphs. I will explain the origin to the following conjecture of Meshulam and me: There is an absolute upper bound for the chromatic number of graphs with no induced cycles of length divisible by 3.
  4. Embedding of 2-dimensional complexes and high dimensional minors. I will discuss the following conjecture: A 2-dimensional simplicial complex with E edges and F 2-dimensional faces that can be embedded into 4-space satisfies F < 4E.
10:30coffee break
11:00 Jörg Rambau (Bayreuth). The Converse
The story of a widely believed fact.
11:30 Volkmar Welker (Marburg). Geometric Combinatorics of Golod Rings and Moment Angle Complexes
To a simplicial complex \Delta on ground set [n] and a pair of spaces (X,A) one associates the generalized moment angle complex or polyhedral product Z_\Delta(X,A) as the subspace of the n-fold product consisting of those tuples for which the set of indices of coordinates in X-A lies in \Delta. In the talk we recall several connections between the topology of moment angle complexes and algebraic properties of the Stanley-Reisner ring of \Delta, in particular Golodness.
12:00lunch break
14:00Martin Grötschel (Berlin) LP/IP Solvers: Are there still challenges?
In this lecture I will provide a survey of the techniques for the solution of linear and mixed-integer optimization problems. I will particularly focus on the algorithmic progress in the last years and show examples of industry applications of breathtaking size that have been solved to optimality. But there are also large scale LPs and small scale IPs that are unsolvable with the current methods. And there is the "exact solution issue". Is anyone interested in exact LP/IP solutions, can one compute these in reasonable time? Do we need new theory, or is current progress just a matter of experimental mathematics? I will indicate some answers.
15:00coffee break
15:30 Volker Kaibel (Magdeburg). Forbidden Vertices
We investigate the question what happens to a polytope when forbidding a list of its vertices and considering the convex hull of the unforbidden ones. Under which conditions does the situation remain tractable in a geometric and/or computational sense? Under which conditions does it not? It turns out that also here 0/1-polytopes behave much nicer than general ones. The talk is based on joint work with Gustavo Angulo, Shabbir Ahmed, and Santanu Dey (Georgia Tech).
16:00Karim Adiprasito (Berlin). New constructions for projectively unique polytopes
The study of projectively unique polytopes is a classic subject in the theory of realization spaces of polytopes, initiated by Perles, Shephard and McMullen. I will present a universality theorem for projectively unique polytopes ("Every polytope is the face of a projectively unique polytope"), and a construction for projectively unique polytopes based on the theory of conjugate nets in differential geometry. These constructions answer problems of Shephard and Perles--Shephard, respectively. This reports on joint work with Arnau Padrol and Guenter M. Ziegler.
16:30Final words and transition to conference dinner


Registration is CLOSED.


The conference will take place at the Konrad-Zuse-Institute in Berlin-Dahlem. Directions can be found here.


Christian Haase       Raman Sanyal       Nadja Wisniewski

we are kindly supported by