BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Drupal iCal API//EN
X-WR-CALNAME:Events items teaser
X-WR-TIMEZONE:America/Toronto
BEGIN:VTIMEZONE
TZID:America/Toronto
X-LIC-LOCATION:America/Toronto
BEGIN:DAYLIGHT
TZNAME:EDT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
DTSTART:20250309T070000
END:DAYLIGHT
BEGIN:STANDARD
TZNAME:EST
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
DTSTART:20241103T060000
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
UID:686c754123b0b
DTSTART;TZID=America/Toronto:20250711T153000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250711T163000
URL:/combinatorics-and-optimization/events/tutte-colloq
 uium-stephen-melczer-0
SUMMARY:Tutte colloquium-Stephen Melczer
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Automated Sequence Asymptotics\n\nSPEAKER:\n 
 Stephen Melczer\n\nAFFILIATION:\n University of À¶Ý®ÊÓƵ\n\nLOCATION:\n MC
  5501\n\nABSTRACT:Computing with any sort of object requires a way of enco
 ding\nit on a computer\, which poses a problem in enumerative combinatoric
 s\nwhere the objects of interest are (infinite) combinatorial sequences.\n
 Thankfully\, the generating function of a combinatorial sequence often\nsa
 tisfies natural algebraic/differential/functional equations\, which\ncan t
 hen be viewed as data structures for the sequence. In this talk\nwe survey
  methods to take a sequence encoded by such data structures\nand automatic
 ally determine asymptotic behaviour using techniques from\nthe field of an
 alytic combinatorics. We also discuss methods to\nautomatically characteri
 ze the asymptotic behaviour of multivariate\nsequences using analytic comb
 inatorics in several variables (ACSV).\nThe focus of each topic will be ri
 gorous algorithms that have already\nbeen implemented in computer algebra 
 systems and can be easily used by\nanyone.\n\n \n 
DTSTAMP:20250708T013249Z
END:VEVENT
BEGIN:VEVENT
UID:686c754125745
DTSTART;TZID=America/Toronto:20250710T143000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250710T153000
URL:/combinatorics-and-optimization/events/algebraic-an
 d-enumerative-combinatorics-seminar-karen-yeats-2
SUMMARY:Algebraic and enumerative combinatorics seminar-Karen Yeats
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Sizes of witnesses in covtree\n\nSpeaker\n Ka
 ren Yeats\n\nAffiliation\n University of À¶Ý®ÊÓƵ\n\nLocation\n MC 5479\n\
 nABSTRACT: Here is a purely combinatorial problem that arose in causal\ns
 et theory.  Let {P_1\, ... \, P_k} be distinct unlabelled posets all\nwit
 h n elements.  Suppose there is a poset Q such that {P_1\, ... \,\nP_k} i
 s exactly the set of downsets of Q of size n up to isomorphism.\nGiven n a
 nd k can we give a tight upper bound on the minimum size of\nsuch a Q? As 
 with newspaper headlines\, the answer to the question is\nno\, at least fo
 r the moment\, but I'll explain what we do know.  Joint\nwork with Jette 
 Gutzeit\, Kimia Shaban\, and Stav Zalel.\n\nTHERE WILL BE A PRE-SEMINAR PR
 ESENTING RELEVANT BACKGROUND AT THE\nBEGINNING GRADUATE LEVEL STARTING AT 
 1:30PM\,\n 
DTSTAMP:20250708T013249Z
END:VEVENT
BEGIN:VEVENT
UID:686c754126960
DTSTART;TZID=America/Toronto:20250703T143000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250703T153000
URL:/combinatorics-and-optimization/events/algebraic-an
 d-enumerative-combinatorics-seminar-farhad
SUMMARY:Algebraic and enumerative combinatorics seminar-Farhad Soltani
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Quasisymmetric Harmonics in Superspace\n\nSpe
 aker\n Farhad Soltani\n\nAffiliation\n York University\n\nLocation\n MC 5
 479\n\nABSTRACT: The harmonics of quasisymmetric polynomials in superspac
 e\nare the  orthogonal complement of the ideal generated by\nquasisymmet
 ric polynomials without constant term. In this talk\, I will\ndiscuss the 
 harmonics and present the first basis of this space\, which\nis indexed by
  a specific family of nested forests.\n\nTHERE WILL BE A PRE-SEMINAR PRESE
 NTING RELEVANT BACKGROUND AT THE\nBEGINNING GRADUATE LEVEL STARTING AT 1:3
 0PM\,\n 
DTSTAMP:20250708T013249Z
END:VEVENT
BEGIN:VEVENT
UID:686c7541277f6
DTSTART;TZID=America/Toronto:20250704T153000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250704T163000
URL:/combinatorics-and-optimization/events/tutte-colloq
 uium-henry-wolkowicz-2
SUMMARY:Tutte colloquium-Henry Wolkowicz
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:The omega-Condition Number: Applications to P
 reconditioning and\nLow Rank Generalized Jacobian Updating\n\nSPEAKER:\n H
 enry Wolkowicz\n\nAFFILIATION:\n University of À¶Ý®ÊÓƵ\n\nLOCATION:\n MC 
 5501\n\nABSTRACT: Preconditioning is essential in iterative methods for\n
 solving linear systems. It is also the implicit objective in updating\napp
 roximations of Jacobians in optimization methods\, e.g.\,~in\nquasi-Newton
  methods. We study a nonclassic matrix condition number\,\nthe omega-condi
 tion number}\, omega for short. omega is the ratio of:\nthe arithmetic and
  geometric means of the singular values\, rather than\nthe largest and sma
 llest for the classical kappa-condition number. The\nsimple functions in o
 mega allow one to exploit  first order\noptimality conditions. We use thi
 s fact to derive explicit formulae\nfor (i) omega-optimal low rank updatin
 g of generalized Jacobians\narising in the context of nonsmooth Newton met
 hods\; and (ii)\nomega-optimal preconditioners of special structure for  
 iterative\nmethods for linear systems. In the latter context\, we analyze 
 the\nbenefits of omega for (a) improving the clustering of eigenvalues\; (
 b)\nreducing the number of iterations\; and (c) estimating the actual\ncon
 dition of a linear system. Moreover we show strong theoretical\nconnection
 s between the omega-optimal preconditioners and incomplete\nCholesky facto
 rizations\, and highlight the misleading effects arising\nfrom the inverse
  invariance of kappa. Our results confirm the efficacy\nof using the omega
 -condition number compared to the kappa-condition\nnumber.\n\n(Joint work 
 with: Woosuk L. Jung\, David Torregrosa-Belen.)\n\n \n 
DTSTAMP:20250708T013249Z
END:VEVENT
BEGIN:VEVENT
UID:686c7541286bc
DTSTART;TZID=America/Toronto:20250626T130000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250626T143000
URL:/combinatorics-and-optimization/events/co-reading-g
 roup-jacob-skitsko-3
SUMMARY:C&O Reading Group -Jacob Skitsko
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE: Fault Tolerant Routing and High Dimensional
  Expanders\n\nSPEAKER:\n Jacob Skitsko\n\nAFFILIATION:\n University of Wat
 erloo\n\nLOCATION:\n MC 6029\n\nABSTRACT: We will go over some recent resu
 lts about fault tolerant\nrouting from Bafna\, Minzer\, Vyas. Two parallel
  series of works from\nthe last few years from Bafna\, Lifshitz\, Minzer\,
  Vyas as well as\nDikstein\, Dinur\, Lubotzky has led to size efficient PC
 Ps by using high\ndimensional expanders. We will comment on the context fo
 r these works\,\nand briefly go over some high level ideas. Then\, we will
  talk about an\napplication to fault tolerant rounding. The goal in this p
 roblem is to\ndesign a sparse network supporting efficient fault tolerant\
 ninteractions between all pairs of nodes. Using the size efficient PCP\nco
 nstruction\, Bafna and Minzer gave a construction of constant degree\nnetw
 orks with efficient protocols that tolerate a constant fraction of\nadvers
 arial edge faults.\n 
DTSTAMP:20250708T013249Z
END:VEVENT
BEGIN:VEVENT
UID:686c7541297ed
DTSTART;TZID=America/Toronto:20250626T143000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250626T153000
URL:/combinatorics-and-optimization/events/algebraic-an
 d-enumerative-combinatorics-seminar-leo-jiang
SUMMARY:Algebraic and enumerative combinatorics seminar-Leo Jiang
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Oriented graded Möbius algebras\n\nSpeaker\n
  Leo Jiang\n\nAffiliation\n University of Toronto\n\nLocation\n MC 5479\n\
 nABSTRACT:The graded Möbius algebra B(M) of a matroid M contains much\nco
 mbinatorial information about the flats of M. Its algebraic\nproperties we
 re instrumental in the proof of the Dowling—Wilson\ntop-heavy conjecture
 . We will introduce a skew-commutative analogue\nOB(M) associated to every
  oriented matroid M\, and discuss its\nalgebraic structure. This is part o
 f ongoing work joint with Yu Li.\n\nTHERE WILL BE A PRE-SEMINAR PRESENTING
  RELEVANT BACKGROUND AT THE\nBEGINNING GRADUATE LEVEL STARTING AT 1:30PM\,
 \n 
DTSTAMP:20250708T013249Z
END:VEVENT
BEGIN:VEVENT
UID:686c75412a92c
DTSTART;TZID=America/Toronto:20250627T153000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250627T163000
URL:/combinatorics-and-optimization/events/tutte-colloq
 uium-gary-au-0
SUMMARY:Tutte colloquium-Gary Au
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Worst-case instances of the stable set proble
 m of graphs for the\nLovász–Schrijver SDP hierarchy\n\nSPEAKER:\n Gary 
 Au\n\nAFFILIATION:\n University of Saskatchewan\n\nLOCATION:\n MC 5501\n\n
 ABSTRACT:(Based on joint work with Levent Tunçel.)\n\nIn this talk\, we d
 iscuss semidefinite relaxations of the stable set\nproblem of graphs gener
 ated by the lift-and-project operator LS_+ (due\nto Lovász and Schrijver)
 \, and present some of our recent progress on\nthis front. In particular\,
  we show that for every positive integer k\,\nthe smallest graph with LS_+
 -rank k contains exactly 3k vertices. This\nresult is sharp and settles a 
 conjecture posed by Lipták and Tunçel\nfrom 2003.\n\nThe talk will be ac
 cessible to a general audience\, and does not assume\nany prior knowledge 
 of lift-and-project methods.\n\n \n 
DTSTAMP:20250708T013249Z
END:VEVENT
BEGIN:VEVENT
UID:686c75412c211
DTSTART;TZID=America/Toronto:20250619T130000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250619T143000
URL:/combinatorics-and-optimization/events/co-reading-g
 roup-nikhil-kumar-1
SUMMARY:C&O Reading Group -Nikhil Kumar
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE: Almost Tight Additive Guarantees for k-Edge
 -Connectivity\n\nSPEAKER:\n Nikhil Kumar\n\nAFFILIATION:\n University of W
 aterloo\n\nLOCATION:\n MC 6029\n\nABSTRACT: We consider the k-edge-connect
 ed spanning subgraph (k-ECSS)\nproblem\, where we are given an undirected 
 graph G = (V\, E) with\nnonnegative edge costs\, and the goal is to find a
  minimum-cost\nsubgraph H of G that is k-edge-connected\; that is\, there 
 exist at\nleast k edge-disjoint paths between every pair of vertices in H.
 \n\nFor even k\, we present a polynomial-time algorithm that computes a\n(
 k−2)-edge-connected subgraph whose cost is at most that of the\nnatural 
 LP relaxation of k-ECSS. I will try to present an overview of\nour algorit
 hm and analysis\, which is based on the iterative rounding\ntechnique.\n 
DTSTAMP:20250708T013249Z
END:VEVENT
BEGIN:VEVENT
UID:686c75412da7a
DTSTART;TZID=America/Toronto:20250620T153000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250620T163000
URL:/combinatorics-and-optimization/events/tutte-colloq
 uium-sepehr-hajebi
SUMMARY:Tutte colloquium-Sepehr Hajebi
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:Complete bipartite induced minors (and treewi
 dth)\n\nSPEAKER:\n Sepehr Hajebi\n\nAFFILIATION:\n University of À¶Ý®ÊÓƵ\
 n\nLOCATION:\n MC 5501\n\nABSTRACT:I will present a result that describes 
 the unavoidable\ninduced subgraphs of graphs with a large complete biparti
 te induced\nminor\, and will discuss the connections and applications to b
 ounding\nthe treewidth in hereditary classes of graphs. If time permits\, 
 I will\nalso sketch some proofs.\n\n Joint work with Maria Chudnovsky and
  Sophie Spirkl.\n\n \n 
DTSTAMP:20250708T013249Z
END:VEVENT
BEGIN:VEVENT
UID:686c75412f28e
DTSTART;TZID=America/Toronto:20250619T143000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20250619T153000
URL:/combinatorics-and-optimization/events/algebraic-an
 d-enumerative-combinatorics-seminar-elana
SUMMARY:Algebraic and enumerative combinatorics seminar-Elana Kalashnikov
CLASS:PUBLIC
DESCRIPTION:Summary \n\nTITLE:The Abelian/non-Abelian correspondence and Li
 ttlewood-Richardson\n\n\nSpeaker\n Elana Kalashnikov\n\nAffiliation\n Univ
 ersity of À¶Ý®ÊÓƵ\n\nLocation\n MC 5479\n\nABSTRACT:The Abelian/non-Abeli
 an correspondence gives rise to a\nnatural basis for the cohomology of fla
 g varieties\, which - except for\nGrassmannians - is distinct from the Sch
 ubert basis. I will describe\nthis basis and its multiplication rules\, an
 d explain how to relate it\nto the Schubert basis for two-step flag variet
 ies. I will then explain\nhow this leads to new tableaux Littlewood--Richa
 rdson rules for many\nproducts of Schubert classes. This is joint work (se
 parately) with Wei\nGu and Linda Chen.\n\nTHERE WILL BE A PRE-SEMINAR PRES
 ENTING RELEVANT BACKGROUND AT THE\nBEGINNING GRADUATE LEVEL STARTING AT 1:
 30PM\,\n 
DTSTAMP:20250708T013249Z
END:VEVENT
END:VCALENDAR