The seminar is on Thursdays at 11:00 AM in Bradley 105.
The seminar will be followed by the Thursday Lunch Expedition.
May 19, 2006
Christophe Hohlweg (The Fields Institute, University
of TOronto)
Title: Realizations of the associahedron
and cyclohedron
SPECIAL ROOM: Bradley 104 and TIME: 4:00 PM
Abstract: We describe different realizations with integer coordinates for
the associahedron (i.e., the Stasheff polytope) and for the cyclohedron
(i.e., the Bott-Taubes polytope), and compare them to the permutahedra of
type $A$ and $B$, respectively.
The coordinates are integral and obtained by an algorithm which uses an
oriented Coxeter graph of type $A$ or $B$ respectively as the only input and
which specializes to a procedure presented by J.-L. Loday for a certain
orientation of the Coxeter graph of $A_n$.
The described realizations have cambrian fans of type $A$ and $B$ as normal
fans. This settles a conjecture of N. Reading for cambrian fans of these
types.
This is a joint work with Carsten Lange.
May 17, 2006
Peter Winkler (Dartmouth)
Title: Non-Transitive Dice II
Abstract: Continuation of Non-Transitive Dice from last Thurday, with special
presentation by Annalies Vuong that the upper bound for the size of a dominating
set for a 2-majority tournament is 3.
May 11, 2006
Peter Winkler (Dartmouth)
Title: Non-Transitive Dice
Abstract: Starting with an old scam, we will see how some modern
combinatorial methods
(including VC-dimension) can be used to attack problems in
graph theory and geometry.
The intention is to go slowly and take 2 or 3 weeks as
necessary.
April 13, 2006
Carsten Lange (University of Washington)
Title: Lower bounds for chromatic number
Abstract: A famous problem is the 4-colour problem: How many colours do we need
to colour the countries of a map such that two neighbouring countries are
always assigned different colours?
This task to find the chromatic number of a (hyper-)graph is very hard.
Lovasz introduced a ``topological method'' to obtain lower bounds. I will
introduce this subject and discuss the method.
If you are intenterested in speaking please email Rosa.C.Orellana "at" Dartmouth "dot" edu
This
page is maintained by Rosa
Orellana