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DTSTART:20240310T070000
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TZOFFSETFROM:-0400
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DTSTART:20241103T060000
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BEGIN:VEVENT
UID:67363d62515fb
DTSTART;TZID=America/Toronto:20241118T113000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241118T123000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-gr
aph-theory-shengtong-zhang
SUMMARY:Algebraic Graph Theory-Shengtong Zhang
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE: Squares of eigenvalues and semi-definite opt
imization\n\nSPEAKER:\n Shengtong Zhang\n\nAFFILIATION:\n Stanford Univers
ity\n\nLOCATION:\n Please contact Sabrina Lato for Zoom link.\n\nABSTRAC
T: I will share some recent progress on two long-standing\nconjectures in
spectral graph theory\, namely the\nElphick-Farber-Goldberg-Wocjan conject
ure and the\nBollob\\'{a}s-Nikiforov conjecture. Both conjectures involve
bounds on\nthe sum of squares of the eigenvalues of a graph\, and a key in
gredient\nin our work is the interpretation of such sums as optimization\n
problems involving semi-definite matrices. Part of the talk is joint\nwork
with Gabriel Coutinho and Thomás Jung Spier.\n
DTSTAMP:20241114T181146Z
END:VEVENT
BEGIN:VEVENT
UID:67363d62522d7
DTSTART;TZID=America/Toronto:20241122T153000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241122T163000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/tutte-colloq
uium-kate-larson
SUMMARY:Tutte colloquium-Kate Larson
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE: Soft Condorcet Optimization\n\nSPEAKER:\n Ka
te Larson\n\nAFFILIATION:\n University of Waterloo\n\nLOCATION:\n MC 5501\
n\nABSTRACT:\n\nA common way to drive the progress of AI models and agents
is to\ncompare their performance on standardized benchmarks. This often\n
involves aggregating individual performances across a potentially wide\nva
riety of tasks and benchmarks and many of the leaderboards that draw\ngrea
test attention are Elo-based. \n\n \n\nIn this paper\, we describe a nov
el ranking scheme inspired by social\nchoice frameworks\, called Soft Cond
orcet Optimization (SCO)\, to\ncompute the optimal ranking of agents: the
one that makes the fewest\nmistakes in predicting the agent comparisons in
the evaluation data.\nThis optimal ranking is the maximum likelihood esti
mate when\nevaluation data (which we view as votes) are interpreted as noi
sy\nsamples from a ground truth ranking\, a solution to Condorcet's\norigi
nal voting system criteria and inherits desirable social-choice\ninspired
properties since SCO ratings are maximal for Condorcet\nwinners when they
exist\, which we show is not necessarily true for the\nclassical rating sy
stem Elo.\n\n \n\nWe propose three optimization algorithms to compute SCO
ratings and\nevaluate their empirical performance across a variety of syn
thetic and\nreal-world datasets\, to illustrate different properties.\n\n
\n\nWith Marc Lanctot\, Ian Gemp\, Quentin Berthet\, Yoram Bachrach\, Ma
nfred\nDiaz\, Roberto-Rafael Maura-Rivero\, Anna Koop\, and Doina Precup
\n\n \n\n \n
DTSTAMP:20241114T181146Z
END:VEVENT
BEGIN:VEVENT
UID:67363d6252cd4
DTSTART;TZID=America/Toronto:20241115T153000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241115T163000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/tutte-colloq
uium-guoyin-li
SUMMARY:Tutte colloquium-Guoyin Li
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE: Proximal methods for nonsmooth and nonconvex
fractional\nprograms: when sparse optimization meets fractional programs\
n\nSPEAKER:\n Guoyin Li\n\nAFFILIATION:\n University of New South Wales \n
\nLOCATION:\n MC 5501\n\nABSTRACT:Nonsmooth and nonconvex fractional progr
ams are ubiquitous\nand also highly challenging. It includes the composite
optimization\nproblems studied extensively lately\, and encompasses many
important\nmodern optimization problems arising from diverse areas such as
the\nrecent proposed scale invariant sparse signal reconstruction problem
\nin signal processing\, the robust Sharpe ratio optimization problems in\
nfinance and the sparse generalized eigenvalue problem in\ndiscrimination
analysis. \n\nIn this talk\, we will introduce extrapolated proximal metho
ds for\nsolving nonsmooth and nonconvex fractional programs and analyse th
eir\nconvergence behaviour. Interestingly\, we will show that the proposed
\nalgorithm exhibits linear convergence for the scale invariant sparse\nsi
gnal reconstruction model\, and the sparse generalized eigenvalue\nprobl
em with either cardinality regularization or sparsity\nconstraints. This i
s achieved by identifying the explicit\ndesingularization function of the
Kurdyka-_Ł_ ojasiewicz inequality\nfor the merit function of the fraction
al optimization models. Finally\,\nif time permits\, we will present some
preliminary encouraging\nnumerical results for the proposed methods for sp
arse signal\nreconstruction and sparse Fisher discriminant analysis\n\nThe
talk is based on joint work with R.I. Bo ̧t\, M. Dao\, T.K. Pong\nand P.
Yu.\n\n \n\n \n
DTSTAMP:20241114T181146Z
END:VEVENT
BEGIN:VEVENT
UID:67363d6253672
DTSTART;TZID=America/Toronto:20241107T140000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241107T150000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-an
d-enumerative-combinatorics-seminar-stephan
SUMMARY:Algebraic and enumerative combinatorics seminar-Stephan\nPfannerer-
Mittas
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Descents for Border Strip Tableaux\n\nSpeaker
\n Stephan Pfannerer-Mittas\n\nAffiliation\n University of Waterloo\n\nLoc
ation\n MC 5479\n\n ABSTRACT: Lusztig's fake degree is the generating pol
ynomial for the\nmajor index of standard Young tableaux of a given shape.
Results of\nSpringer and James & Kerber imply that\, mysteriously\, its ev
aluation\nat a d-th primitive root of unity yields the number of border st
rip\ntableaux with all strips of size d\, up to sign. This is essentially\
nthe special case of the Murnaghan-Nakayama rule for rectangular\npartitio
ns as cycle type. We refine this result to standard Young\ntableaux and bo
rder strip tableaux with a given number of descents. To\ndo so\, we introd
uce a new descent statistic for border strip tableaux\,\nextending the cla
ssical definition for standard Young tableaux.\n\nTHERE WILL BE A PRE-SEMI
NAR PRESENTING RELEVANT BACKGROUND AT THE\nBEGINNING GRADUATE LEVEL STARTI
NG AT 1PM\,\n
DTSTAMP:20241114T181146Z
END:VEVENT
BEGIN:VEVENT
UID:67363d6253d84
DTSTART;TZID=America/Toronto:20241108T153000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241108T163000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/tutte-colloq
uium-r-tyrell-rockafellar
SUMMARY:Tutte colloquium-R. Tyrell Rockafellar
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE: Problem Decomposition in Optimization: Alg
orithmic Advances\nBeyond ADMM\n\nSPEAKER:\n R. Tyrell Rockafellar\n\nAFFI
LIATION:\n The University of Washington\n\nLOCATION:\n Main Hall\, Federat
ion Hall \n\nABSTRACT: \n\nDecomposition schemes like those coming from AD
MM typically start by\nposing a separable-type problem in the Fenchel dual
ity format. They\nthen pass to an augmented Lagrangian\, which however c
an interfere with\nthe separability and cause a slow-down. Progressive d
ecoupling\noffers a more flexible approach which can utilize augmented\nLa
grangians while maintaining decomposability. Based on a variable\nmetric
extension of the proximal point algorithm that's applied in a\ntwisted so
rt of way\, progressive decoupling benefits from stopping\ncriteria which
can guarantee convergence despite inexact minimization\nin each iteration.
The convergence is generically at a linear\nrate\, and for convex pro
blems\, is global. But the method also works\nfor nonconvex problems when
initiated close enough to a point that\nsatisfies a natural extension of t
he strong sufficient condition for\nlocal optimality known from nonlinear
programming. \n\nThis talk is held as part of the 26th Annual Midwest Opti
mization\nMeeting (“MOM26”).\n\n \n
DTSTAMP:20241114T181146Z
END:VEVENT
BEGIN:VEVENT
UID:67363d6254544
DTSTART;TZID=America/Toronto:20241114T140000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241114T150000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-an
d-enumerative-combinatorics-seminar-colleen
SUMMARY:Algebraic and enumerative combinatorics seminar-Colleen Robichaux
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Vanishing of Schubert coefficients\n\nSpeaker
\n Colleen Robichaux\n\nAffiliation\n UCLA\n\nLocation\n MC 5479\n\n ABST
RACT: Schubert coefficients are nonnegative integers that arise\nin Algebr
aic Geometry and play a central role in Algebraic\nCombinatorics. It is a
major open problem whether they have a\ncombinatorial interpretation\, i.e
\, they are in #P. In this talk we\ndiscuss the closely related problem of
the vanishing of Schubert\ncoefficients. We prove that this vanishing pro
blem is rather low in\nthe polynomial hierarchy and discuss implications o
f this result.\n\nThis is joint work with Igor Pak.\n\nTHERE WILL BE A PRE
-SEMINAR PRESENTING RELEVANT BACKGROUND AT THE\nBEGINNING GRADUATE LEVEL S
TARTING AT 1PM\,\n
DTSTAMP:20241114T181146Z
END:VEVENT
BEGIN:VEVENT
UID:67363d6254bc8
DTSTART;TZID=America/Toronto:20241104T113000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241104T123000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-gr
aph-theory-he-guo
SUMMARY:Algebraic Graph Theory-He Guo
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE: Intersection of Matroids\n\nSPEAKER:\n He Gu
o\n\nAFFILIATION:\n Umeå University\n\nLOCATION:\n Please contact Sabrin
a Lato for Zoom link.\n\nABSTRACT: We study simplicial complexes (hypergr
aphs closed under\ntaking subsets) that are the intersection of a given nu
mber k of\nmatroids. We prove bounds on their chromatic numbers (the minim
um\nnumber of edges required to cover the ground set) and their list\nchro
matic numbers. Settling a conjecture of Kiraly and\nBerczi--Schwarcz--Yama
guchi\, we prove that the list chromatic number\nis at most k times the ch
romatic number. The tools used are in part\ntopological. If time permits\,
I will also discuss a result proving\nthat the list chromatic number of t
he intersection of two matroids is\nat most the sum of the chromatic numb
ers of each matroid\, improving a\nresult by Aharoni and Berger from 2006.
The talk is based on works\njoint with Ron Aharoni\, Eli Berger\, and Dan
iel Kotlar. In this talk\,\nthere is no assumption about background knowle
dge of matroid theory or\nalgebraic topology.\n
DTSTAMP:20241114T181146Z
END:VEVENT
BEGIN:VEVENT
UID:67363d6255296
DTSTART;TZID=America/Toronto:20241031T140000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241031T150000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-an
d-enumerative-combinatorics-seminar-joseph
SUMMARY:Algebraic and enumerative combinatorics seminar-Joseph Fluegemann
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Smooth points on positroid varieties and plan
ar N=4\nsupersymmetric Yang-Mills theory\n\nSpeaker\n Joseph Fluegemann\n\
nAffiliation\n University of Waterloo\n\nLocation\n MC 5479\n\n ABSTRACT:
Positroid varieties are subvarieties in the Grassmannian\ndefined by cycl
ic rank conditions and which are related to Schubert\nvarieties. We will p
rovide a criterion for whether positroid varieties\nare smooth at certain
distinguished points\, and we will show that this\ninformation is sufficie
nt to determine smoothness for the entire\npositroid variety. This will in
volve looking at combinatorial diagrams\ncalled \"affine pipe dreams.\" We
can also form a partial order on\npositroid varieties given by deletion a
nd contraction\, such that there\nis closure for smooth positroid varietie
s\, and we will characterize\nthe minimal singular elements in this order.
Finally\, we will discuss\na couple of connections between the techniques
of this work and planar\nN=4\n\nSYM: the BCFW bridge decomposition and in
verse soft factors.\n\nTHERE WILL BE A PRE-SEMINAR PRESENTING RELEVANT BAC
KGROUND AT THE\nBEGINNING GRADUATE LEVEL STARTING AT 1PM\,\n
DTSTAMP:20241114T181146Z
END:VEVENT
BEGIN:VEVENT
UID:67363d62558ed
DTSTART;TZID=America/Toronto:20241028T113000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241028T123000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-gr
aph-theory-roberto-hernandez-palomares
SUMMARY:Algebraic Graph Theory-Roberto Hernández Palomares
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE: Quantum graphs\, subfactors and tensor categ
ories\n\nSPEAKER:\n Roberto Hernández Palomares\n\nAFFILIATION:\n Univers
ity of Waterloo\n\nLOCATION:\n Please contact Sabrina Lato for Zoom link
.\n\nABSTRACT: Graphs and their noncommutative analogues are interesting\n
objects of study from the perspectives of operator algebras\, quantum\ninf
ormation and category theory. In this talk we will introduce\n equivarian
t graphs with respect to a quantum symmetry along with\nexamples such as c
lassical graphs\, Cayley graphs of finite groupoids\,\nand their quantum a
nalogues. We will also see these graphs can be\nconstructed concretely by
modeling a quantum vertex set by an\ninclusion of operator algebras and th
e quantum edge set by an\nequivariant endomorphism that is an idempotent w
ith respect to\nconvolution/Schur product. Equipped with this viewpoint an
d tools from\nsubfactor theory\, we will see how to obtain all these idemp
otents\nusing higher relative commutants and the quantum Fourier transform
.\nFinally\, we will state a quantum version of Frucht's Theorem\, showing
\nthat every quasitriangular finite quantum groupoid arises as certain\nau
tomorphisms of some categorified graph.\n
DTSTAMP:20241114T181146Z
END:VEVENT
BEGIN:VEVENT
UID:67363d6255faa
DTSTART;TZID=America/Toronto:20241025T123000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20241025T133000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/co-reading-g
roup-parth-mittal
SUMMARY:C&O Reading Group - Parth Mittal
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Nearly optimal communication and query comple
xity of bipartite\nmatching \n\nSPEAKER:\n Parth Mittal\n\nAFFILIATION:\n
University of Waterloo\n\nLOCATION:\n MC 6029\n\nABSTRACT:I will talk abo
ut a recent paper (Blikstad\, van den Brand\,\nEfron\, Mukhopadhyay\, Nano
ngkai\, FOCS 22) which gives near-optimal\nalgorithms for bipartite matchi
ng (and several generalizations) in\ncommunication complexity\, and severa
l types of query complexity. We\nwill focus only on the simplest case (i.e
. unweighted bipartite\nmatching)\,and will not assume any background on c
ommunication or query\ncomplexity.\n
DTSTAMP:20241114T181146Z
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