You are cordially invited to our next Monday Lecture &
Colloquium on July 16th at 14:15 h & 16:00 h at TU Berlin. Location: Technische Universität Berlin Straße des 17. Juni 136 10623 Berlin Time: Monday, July 16th - 14:15 h Lecture: Mihyun Kang (Graz University of Technology) Title: Vanishing of cohomology groups of random
simplicial complexes We consider
random simplicial complexes that are generated from the binomial
random hypergraphs by taking the downward-closure. We determine
when all cohomology groups with coefficients in F_2 vanish. This
is joint work with Oliver Cooley, Nicola Del Giudice, and Philipp
Spruessel.
Coffee & Tea Break : Room MA 316 - Third Floor Technische Universität Berlin Straße des 17. Juni 136 10623 Berlin Time: Monday, July 16th - 16:00 h Colloquium: Martin Balko (Charles
University of Prague) Title: Ramsey numbers and monotone colorings For positive integers N and r >= 2, an r-monotone coloring of r-tuples from [N] is a 2-coloring by -1 and +1 that is monotone on the lexicographically ordered sequence of r-tuples of every (r+1)-tuple from [N]. Let ORS(n;r) be the minimum N such that every r-monotone coloring of r tuples from [N] contains n elements with all r-tuples of the same color. For every r >= 3, it is known that ORS(n;r) is bounded from above by a tower function of height r-2 with O(n) on the top. The Erdős--Szekeres Lemma and the Erdős--Szekeres Theorem imply ORS(n;2)=(n-1)^{^2}+1 and ORS(n;3) = ((2n-4) choose (n-2))+1, respectively. It follows from a result of Eliáš and Matoušek that ORS (n;4) grows as o tower of height 2. We show that ORS(n;r) grows at least as a tower of height r-2 for every r >= 3. This, in particular, solves an open problem posed by Eliáš and Matoušek and by Moshkovitz and Shapira. Using two geometric interpretations of monotone colorings, we show connections between estimating ORS(n;r) and two Ramsey-type problems that have been recently considered by several researchers. We also prove asymptotically tight estimates on the number of r-monotone colorings. -- Graduiertenkolleg 'Facets of Complexity' www.facetsofcomplexity.de/monday |