The University of Michigan Combinatorics Seminar
Past Seminars (2000 - present)

Seminar organizers: Sergey Fomin (2000-present), Mark Skandera (2000-03), Patricia Hersh (2003-04), Nathan Reading (2004-06), Kyle Petersen (2006-).

Fall 2007

date speaker affiliation title (click for an abstract)
September 14 Lauren Williams Harvard Toric geometry and the totally non-negative part of G/P
September 21 Hannah Markwig U. Michigan Counting plane elliptic tropical curves with fixed j-invariant
September 28 Brendon Rhoades U. Minnesota Cyclic sieving, promotion, and representation theory
October 5 Harm Derksen U. Michigan Mutations of quivers
October 12 Matjaž Konvalinka MIT Non-commutative extensions of the MacMahon master theorem
October 19 Vladimir Retakh Rutgers Algebras associated to directed acyclic graphs
October 26 Michael Shapiro MSU On double Hurwitz numbers in genus 0
November 1 Leonid Chekhov Steklov Inst. Teichmüller theory of bordered surfaces
November 2 Dylan Thurston Columbia Characterizing generic global rigidity
November 9 Alexander Gamburd UCSC/IAS Expanders: from arithmetic to combinatorics and back
November 16 Roman Vershynin UC Davis Randomness in functional analysis: toward universality
November 30 Keith Ball UCL Plank and coefficient problems
December 7 Jan Vondrák Princeton Approximation algorithms for combinatorial allocation problems

Winter 2007

date speaker affiliation title (click for an abstract)
January 19
John Stembridge U. Michigan Irreducible circuits and Coxeter arrangements
January 26
Julianna Tymoczko U. Michigan Divided difference operators in the equivariant cohomology of Grassmannians
February 2
Petter Brändén U. Michigan Some applications of polynomials with the half-plane property
February 9
Sara Billey U. Washington Embedded factor patterns for Deodhar elements in Kazhdan-Lusztig theory
February 16
Martin Strauss U. Michigan One sketch for all: Fast algorithms for compressed sensing
March 9
 Alexander Yong U. Minnesota Cominuscule Schubert calculus and tableau combinatorics
March 23
David Wilson Microsoft Boundary partitions in trees and dimers
March 30
Hugh Thomas U. New Brunswick (Co)minuscule Schubert Calculus
April 6
Ira Gessel Brandeis U. Counting permutations by putting balls into boxes
April 13
Thomas Lam Harvard Temperley-Lieb pfaffinants

Fall 2006

date speaker affiliation title (click for an abstract)
September 8
Grigory Mikhalkin U. Toronto Curves in Pn: inductive enumeration by dimension
September 15
Alexander Barvinok U. Michigan Counting contingency tables and integer flows
September 22
Peter McNamara Bucknell When are two skew Schur functions equal?
September 29
Nathan Reading NC State Sortable elements and Cambrian fans
October 6
Pavlo Pylyavskyy MIT Poset generating functions and log-supermodularity
October 20
David Speyer Clay/Michigan Decompositions of matroid polytopes and a new matroid invariant
October 27
Kyle Petersen U. Michigan The Hopf algebra of posets
November 3
Ellen Veomett U. Michigan The computational complexity of convex bodies
November 10
 Maria Chudnovsky Columbia/Clay Cycles in dense digraphs
November 17
 Mihai Ciucu Georgia Tech The emergence of the electrostatic field as a Feynman sum in random tilings with holes
December 1
Benny Sudakov Princeton Pseudo-random graphs: properties and applications

Winter 2006

date speaker affiliation title (click for an abstract)
February 17 Satyan Devadoss Williams College Configuration spaces, Coxeter operads, and graph-associahedra
March 10 Patricia Hersh Indiana University The q=-1 phenomenon via homology concentration
March 24 Roy Meshulam Technion Helly type theorems for Leray complexes
March 31 Cristian Lenart SUNY Albany Generalizing the combinatorics of Young tableaux to arbitrary Lie type
April 7 Harm Derksen U. Michigan Quivers and LR-coefficients
April 14 Petter Brändén U. Michigan The support of polynomials with the half-plane property

Fall 2005 (also this term: the Tropical Geometry Seminar)

date speaker affiliation title (click for an abstract)
September 21
(Alg.Geom.) 		Harm Derksen U. Michigan Quivers and combinatorics
October 21
Alexandru Nica U. Waterloo A direct bijection for the Harer-Zagier formula
October 28
 Mike Develin AIM Tropical polytopes and their implications
December 9
Christophe Hohlweg Fields Institute A Loday's realization for the cyclohedron

Winter 2005

date speaker affiliation title (click for an abstract)
January 7
Jason Fulman U. Pittsburgh Stein's method for combinatorialists
January 17
(joint w/Alg. Geo.) 		Anders Buch Aarhus U. A formula for non-equioriented quiver orbits
January 21
Nathan Reading U. Michigan Clusters, diminishing elements and noncrossing partitions
January 28
Alexander Barvinok U. Michigan Counting contingency tables and 0-1 matrices
February 4
Sergey Fomin U. Michigan Generalized cluster complexes and Coxeter combinatorics
February 18
Alexander Yong UC Berkeley A formula for K-theoretic truncation Schubert calculus
March 11
Mark Haiman UC Berkeley A combinatorial formula for Macdonald polynomials
March 18
David Speyer UC Berkeley Combinatorial models for the octahedron and cube recurrences
April 1
Satya Lokam U. Michigan Quadratic lower bounds on matrix rigidity
April 8
 Boris Pittel Ohio State How frequently are two permutations comparable in Bruhat order?

Fall 2004

date speaker affiliation title (click for an abstract)
September 10
Lauren Williams MIT The totally nonnegative part of a Grassmannian,
and a q-analogue of the Eulerian numbers
September 17
Julianna Tymoczko U. Michigan Exponents for B-stable ideals
September 24
Ezra Miller U. Minnesota Unfolding polytopes
October 1
 Sam Hsiao U. Michigan Canonical characters on quasisymmetric functions
and bivariate Catalan numbers
October 8
 Sergi Elizalde* MSRI Refined enumeration of pattern-avoiding permutations
October 15 Mihai Ciucu Georgia Tech Holes in random tilings with periodic boundary conditions
interact like charges in electrostatics
October 22 Allen Knutson UC Berkeley Gluing Young tableaux into a ball
October 27
(Wednesday)		 George Andrews Penn State Partitions with short sequences and Ramanujan's mock theta functions
October 29 David Speyer* UC Berkeley Combinatorics of tropical linear spaces
November 5 Leonardo Mihalcea U. Michigan Equivariant quantum Schubert calculus
November 12 Michael Shapiro Michigan State Rational functions and real Schubert calculus
November 19 John Stembridge U. Michigan Explicit matrices for the irreducible representations of Weyl groups
November 29
(joint w/GTLT) 		Andrei Zelevinsky Northeastern U. 1. Total positivity in double Bruhat cells: a precursor to cluster algebras
2. Cluster algebras and their quantizations
November 30
(colloquium) 		Andrei Zelevinsky Northeastern U. Cartan-Killing classification: old and new
December 3 François Bergeron UQAM Positive differences of products of Schur functions

Winter 2004

date speaker affiliation title (click for an abstract)
January 9
Victor Kreiman Michigan State A generalization of the Robinson-Schensted-Knuth correspondence
January 16
Anders Buch Aarhus U. Alternating signs of quiver coefficients
January 23
David Speyer UC Berkeley Tropical linear spaces and the tropical Grassmannian
January 30 Jennifer Morse U. Miami q,t-Kostka polynomials and the affine Weyl group
February 6
Jeffrey Lagarias AT&T Labs Approximate squaring and other iterations
February 13 Peter Hästö U. Michigan Packing density of permutations, patterns and words
February 20 Boris Shapiro U. Stockholm On polynomial families satisfying linear ODE or finite recurrence relations
March 5
Greg Blekherman U. Michigan Convex geometry of orbits
March 12 Marcelo Aguiar Texas A&M Hopf algebras related to symmetric functions
March 19 Divakar Viswanath U. Michigan Shuffling cards for black-jack and other card games
March 26 Frank Sottile Clay Mathematical Institute and MSRI Lower bounds for real polynomial systems from sign-imbalanced posets
April 2 Alek Vainshtein U. Haifa Counting connected components of an intersection of real Schubert cells, and beyond
April 9 Caroline Klivans Cornell The Bergman complex of a matroid and phylogenetic trees
April 16 Edward Swartz Cornell Convex ear decompositions

Fall 2003

date speaker affiliation title (click for an abstract)
September 5 Sam Hsiao U. Michigan Enumerating chains of signed order ideals
September 12 Nathan Reading U. Michigan Cambrian Lattices
September 17-19
(Keeler Lectures) 		Allen Knutson UC Berkeley Positivity, Effectivity, and Degeneration
September 26 Peter Magyar Michigan State Littelmann paths, miniscule representations and affine Lie algebras
September 30
(colloquium)		 Claire Kenyon École Polytechnique Metric Clustering
October 3 Sinai Robins Temple U. Solid angles and theta functions on polytopes
October 7
(colloquium)		 Richard Kenyon Orsay & Princeton Asymptotics of random discrete interfaces
October 10 Mihai Ciucu Georgia Tech A random tiling model for two dimensional electrostatics
October 17 Imre Bárány Renyi Inst. & UCL The fractional Helly number for convex lattice sets
October 24 John Stembridge U. Michigan Graded multiplicities in the Macdonald kernel and a (q,t)-coinvariant algebra
October 31 Bruce Sagan Michigan State Topological properties of active orders for matroid bases
November 7 Boris Pittel Ohio State On dimensions of a random solid diagram
November 14
(joint w/ Comm.Alg.)		 Irena Peeva Cornell Hilbert schemes and flips
November 21 Scott Kravitz U. Michigan Stability of the homology of a filtered Boolean algebra
December 5 Patricia Hersh U. Michigan A GLn(q)-analogue of the partition lattice

Winter 2003

date speaker affiliation title (click for an abstract)
January 10
Kevin Woods U. Michigan The Frobenius problem and generating functions
January 17
Hugh Thomas Fields Institute The higher Stasheff-Tamari posets and the higher Bruhat orders
January 24
Jason Bell U. Michigan Cohen-Macaulay rings and polynomials with real zeros
January 31 John Shareshian Washington U. Analogues of the Lie representation for classical groups
February 7
Alexander Barvinok U. Michigan Random weighting, asymptotic counting and inverse isoperimetry
February 12
(joint w/Alg. Geo.)		 Julianna Tymoczko Princeton An introduction to Hessenberg varieties
February 14 Michael Zabrocki York U. More fermionic formulae
February 19
(joint w/Alg. Geo.)		 William Fulton,
Sergey Fomin		 U. Michigan Eigenvalues, singular values, and Schubert calculus
March 7
Dennis Stanton U. Minnesota q-binomial coefficients and cyclic groups
March 14 Boris Shapiro Stockholm U. Parking functions for graphs, monotone monomial ideals, and their deformations
March 21 Ravi Vakil Stanford A geometric Littlewood-Richardson rule
March 28 Richard Stanley MIT Sign-balanced and maj-balanced posets
April 4 Cristian Lenart SUNY Albany The K-theory of the flag variety and the Fomin-Kirillov quadratic algebra
April 11 Robert Proctor U. North Carolina Jeu de taquin posets and the Littlewood-Richardson Rule

Fall 2002

date speaker affiliation title (click for an abstract)
September 6 Patricia Hersh U. Michigan Optimizing discrete Morse functions
September 13 Sam Hsiao Cornell Structure of the peak Hopf algebra
September 20 Ezra Miller MSRI Gröbner geometry of Schubert polynomials
September 26
(joint w/Comm.Alg.) 		Victor Reiner U. Minnesota On the Charney-Davis and Neggers-Stanley Conjectures
October 4 Robin Forman Rice A topological approach to the game of "20 questions"
October 11 Bogdan Ion U. Michigan The positivity of Kostka-Foulkes polynomials
October 18 Graham Denham U. W. Ontario Equivariant Euler characteristics of discriminants of reflection groups
October 25 Mark Shimozono Virginia Tech Positivity of quiver cycles via deformation
October 30
(joint w/Alg.Geom.) 		Grigory Mikhalkin U. Utah Counting holomorphic curves via lattice paths in polygons
November 1 Alexander Yong U. Michigan Schubert polynomials and quiver formulas
November 8 Greg Blekherman U. Michigan Convexity properties of the cone of nonnegative polynomials
November 15 Frank Sottile U. Mass. Combinatorial Hopf algebras
November 22 Louis Billera Cornell Some curious properties of the descent-to-peak map
December 6 Andreas Blass U. Michigan Homology groups and homotopy types of lattices

Winter 2002

date speaker affiliation title (click for an abstract)
January 11
 Ben Morris UC Berkeley Random walks on truncated cubes and sampling knapsack solutions
January 18
 Phil Hanlon U. Michigan Hodge structure for posets
January 25
 Alex Postnikov MIT Grassmann cells and planar networks
February 1 Nathan Reading U. Minnesota Order dimension of supersolvable arrangements
February 5-7
(Rainich Lectures)		 Robert MacPherson IAS Combinatorial description of topological spaces
February 8
Mark Skandera U. Michigan Inequalities satisfied by minors of totally nonnegative matrices
February 15 Alexander Barvinok U. Michigan Estimating the maximum by moments for functions on orbits
February 19
(colloquium)		 Dan Rockmore Dartmouth The underappreciated wreath product
February 20
(joint w/Alg. Geo.)		 Anders Buch MIT Quantum cohomology of Grassmannians
March 1-3
(AMS meeting)		 (various) (various) Special session on algebraic combinatorics
March 6
 Bruce Sagan MSU Graph coloring and symmetric functions in noncommuting variables
March 15 Frédéric Chapoton UQAM Generalized associahedra associated to root systems
March 22 Satyanarayana Lokam U. Michigan Matrix rigidity -- a survey
March 29 Richard Stanley MIT Border strips, codes, and snakes of skew partitions
April 5 Angèle Hamel Wilfred Laurier Labeled trees and input-output permutation pairs for priority queues
April 12 Ira Gessel Brandeis On the WZ method for combinatorial identities
April 19 Eric Babson U. Washington Mixed volumes of hypersimplices
May 8 Andrei Zelevinsky Northeastern U. Generalized associahedra via quiver representations

Fall 2001

date speaker affiliation title (click for an abstract)
September 7 Harm Derksen U. Michigan Record-breaking codes
September 14 Tamon Stephen U. Michigan The distribution of values in the quadratic assignment problem
September 21 Konstanze Rietsch Cambridge U. Quantum cohomology of partial flag varieties and totally positive Toeplitz matrices
September 25
(colloquium) 		Alexandre Eremenko Purdue U. Real Schubert calculus
September 28 Tim Chow Tellabs The Ring Grooming Problem: combinatorial optimization in modern telecommunications networks
October 5 Margaret Bayer U. Kansas Polytopes: general and ordinary
October 12 Sergey Fomin U. Michigan The Laurent phenomenon
October 19 Sara Billey MIT A root system description of pattern avoidance with applications to G/B
October 23
(colloquium) 		Russell Lyons Georgia Tech/
Indiana U. 		Random spanning trees, random walks, and electric networks
October 26 David Wagner U. Waterloo Networks, Polynomials, and Matroids
October 29-31
(Ziwet Lectures) 		Timothy Gowers Cambridge U./
Princeton U. 		Szemeredi's theorem and related results
November 2 Andrei Gabrielov Purdue U. Degrees of real Grassmann varieties
November 9 Patricia Hersh U. Michigan Multiplicity of the trivial representation in rank-selected homology of the partition lattice
November 16 Michelle Wachs U. Miami Homology of Bounded Degree Graph Complexes
November 30 John Stembridge U. Michigan A local characterization of crystal graphs
December 7 Dieter van Melkebeek U. Wisconsin On the Quantum Complexity of Majority
December 14 Eric Rains AT&T New asymptotic bounds for self-dual codes and lattices

Winter 2001

January 9
(colloquium) 		Alexei Borodin (U. Pennsylvania) Harmonic analysis on the infinite symmetric group
January 23
(colloquium) 		Ravi Vakil (M.I.T.) Branched covers of the sphere and the moduli space of curves:
Geometry, physics, representation theory, combinatorics
January 26 Mikhail Kapranov (U. Toronto) Affine analogs of Hall polynomials and S-duality generating functions
February 2 Jim Propp (U. Wisconsin) Somos sequences and bilinear combinatorics
February 5
(special lecture)		 Andrei Okounkov (UC Berkeley) Moduli of curves, billiards, and random partitions
February 16 Christian Haase (UC Berkeley) Perles at Bing's House: Facet Subgraphs of Simple Polytopes
March 8
(special lecture)		 Michael Shapiro (KTH Stockholm) Hurwitz numbers and moduli spaces
March 9 Michael Gekhtman (Notre Dame) Equalities and inequalities associated with bi-diagonal factorization
March 16 Vladimir Retakh (Rutgers U.) Combinatorics of pseudo-roots of noncommutive polynomials
March 23 Frank Sottile (UMass-Amherst) A SAGBI basis for the quantum Grassmannian
March 30 Michael Kleber (M.I.T.) Schur functions, Plucker relations, and type B/C/D analogues.
April 13 Mark de Longueville (U. Minnesota) Topology and combinatorics of subspace arrangements

Fall 2000

September 15 Alexander Klyachko
(Bilkent U.)		 Orbits of a maximal torus in a flag variety
September 22 Gilberto Bini
(U. Michigan) 		Combinatorial cycles on the moduli spaces of pointed stable curves
September 29 William Fulton
(U. Michigan) 		Eigenvalues of majorized Hermitian matrices and Schubert calculus
October 3
(colloquium)		 Van Vu
(Microsoft Research) 		Chernoff type bounds for sums of dependent random variables and their applications
October 6 Rob Donnelly
(Murray State U.) 		Solitary bases for representations of semisimple Lie algebras
October 13 Peter Magyar
(Michigan State U.)		 Bruhat Order for Two Flags and a Line
October 20 Bruce Sagan
(Michigan State U.) 		Pattern Frequency Sequences and Internal Zeros
October 27 Sergey Fomin
(U. Michigan) 		Loop-erased walks and total positivity
November 3 Greg Warrington
(Harvard U.) 		Maximal Singular Loci of Schubert Varieties in Sl(n)/B
November 10 John Stembridge
(U. Michigan) 		Combinatorial Models for Weyl Characters
November 17 Alexander Barvinok
(U. Michigan) 		Geometry and Complexity of Counting
December 1 Levent Tunçel
(U. Waterloo) 		Cones of matrices, combinatorial optimization and successive convex relaxations of nonconvex sets
December 5
(colloquium) 		Gil Kalai
(Hebrew U.) 		The Fourier Transform of Boolean functions
December 8 Oleg Gleizer
(Northeastern U.) 		Explicit solutions of the additive Deligne-Simpson problem and their applications

Winter 2000

January 14 Anne Schilling (M.I.T.) Level-restricted paths
January 21 no seminar AMS meeting
January 28 Anders Buch (M.I.T.) The Grothendieck class of a quiver variety
February 4 Mark Skandera (M.I.T.) An Eulerian partner for inversions
February 11 John Stembridge (U. Michigan) The combinatorics of reduced words for reflections
February 18 Nantel Bergeron (York U.) Non-commutative Pieri operators on posets
February 25 Alexander Barvinok (U. Michigan) On realization of weighted graphs as graphs
of distances between points in Euclidean space
March 10 Tadeusz Józefiak (Math Reviews) Superdeterminants and representations of Lie superalgebras
March 17 Dennis Stanton (U. Minnesota) Integrals and the Rogers-Ramanujan identities
March 24 Alex Samorodnitsky (IAS) On the optimum of Delsarte's linear program
March 31 Arun Ram (U. Wisconsin) Combinatorics of characters of Hecke algebras and Chevalley groups
April 7 David Jackson (U. Waterloo) The b-conjectures and related questions:
Conjectures for maps, coverings and other objects

This page is maintained by Sergey Fomin.