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DTSTART:20260308T070000
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TZOFFSETFROM:-0400
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DTSTART:20261101T060000
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BEGIN:VEVENT
UID:6ae96275b2008
DTSTART;TZID=America/Toronto:20261102T110000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261102T120000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/combopt-read
 ing-group-rian-neogi-approximating-nash-social
SUMMARY:CombOpt Reading Group | Rian Neogi\, Approximating Nash Social Welf
 are\nvia stable polynomials
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n\nRian Neogi\n\nAFFILIATION:\n University of Waterloo
 \n\nROOM:\n MC 6029\n\nABSTRACT: In this talk\, I will go through the pap
 er of \"Nash Social\nWelfare\, Matrix Permanent\, and Stable Polynomials\"
  by Anari\, Oveis\nGharan\, Saberi\, Singh. We will consider the problem o
 f allocating m\nitems to n agents. Each agent has a value v_{ij} for item 
 j. The goal\nis to construct an allocation A_1\,...\,A_n so as to maximize
  the Nash\nsocial welfare \\prod_i \\sum_{j in A_i} v_{ij}. We will prove 
 a simple\n1/e approximation for the problem.\n\nThe techniques involve pro
 ving a generalization of the Van Der Waerden\ntheorem for bounding the per
 manent of a doubly-stochastic matrix. We\nsetup a convex program relaxatio
 n of the problem. Using the\naforementioned theorem\, we show that a simpl
 e rounding procedure on\nthe optimal solution of this program gives the 1/
 e-approximation.
DTSTAMP:20261103T042629Z
END:VEVENT
BEGIN:VEVENT
UID:6ae96275b31dd
DTSTART;TZID=America/Toronto:20261102T150000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261102T160000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/graphs-and-m
 atroids-rutger-campell-gammoids
SUMMARY:Graphs and Matroids | Rutger Campell\, Gammoids
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n Rutger Campell\n\nAFFILIATION:\n University of Water
 loo\n\nROOM:\n MC 6029\n\nABSTRACT: I will give an introductory talk abou
 t one of my favourite\nclasses of matroids: gammoids. These arise as conne
 ctivity to a base\nset of vertices in a digraph.
DTSTAMP:20261103T042629Z
END:VEVENT
BEGIN:VEVENT
UID:6ae96275b3f73
DTSTART;TZID=America/Toronto:20261105T143000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261105T153000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-an
 d-enumerative-combinatorics-seminar-sophie
SUMMARY:Algebraic and Enumerative Combinatorics Seminar | Sophie Rehberg\,\
 nChromatic word-quasisymmetric functions of matroids
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n Sophie Rehberg\n\nAFFILIATION:\n University of Water
 loo\n\nLOCATION:\n MC 5417\n\nABSTRACT: Billera\, Jia\, and Reiner (2009)
  introduced the\nquasisymmetric functions of matroids and showed that this
  defines a\nHopf algebra homomorphism which is a valuative invariant\, i.e
 .\,\nisomorphic matroids have the same quasisymmetric function and\npolyto
 pal decompositions of matroid base polytopes define relations\namong the c
 orresponding quasisymmetric functions. In this project we\nstudy an analog
 ue in non-commuting variables\, the word-quasisymmetric\nfunctions. To eve
 ry matroid M we associate a word-quasisymmetric\nfunction ψ(M) and call t
 his the chromatic word-quasisymmetric\nfunctions of a matroid. Matroids an
 d word-quasisymmetric functions\nform Hopf algebras\, and our map ψ betwe
 en them is a homomorphism. We\nwant to study the kernel\, equivalently the
  image\, of the map ψ from\nmatroids to word-quasisymmetric functions\, t
 hat is\, we would like to\nunderstand which matroids are indistinguishable
  by the chromatic\nword-quasisymmetric functions. The map ψ is not an inv
 ariant\, but we\ncan show that it is valuative. Using Schubert matroids an
 d nested\nmatroids\, special classes of matroids\, we prove a lower bound 
 of 2^d\n− d for the rank of the map ψ from matroids to the chromatic\nw
 ord-quasisymmetric functions in degree d and conjectured the upper\nbound 
 of d! is tight. Recent AI supported work shows that our\nconjecture is tru
 e.\n\nThis is joint work with Raul Penaguiao.\n\nThere will be a pre-semin
 ar presenting relevant background at\nbeginning graduate level starting at
  1:30pm in MC 5417.
DTSTAMP:20261103T042629Z
END:VEVENT
BEGIN:VEVENT
UID:6ae96275b4c32
DTSTART;TZID=America/Toronto:20261104T100000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261104T110000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/crypto-readi
 ng-group-quantum-computing-aodhan-corrigan-how
SUMMARY:Crypto Reading Group on quantum computing | Aodhan Corrigan\, How t
 o\nrealize a QKD protocol? Imperfections and considerations in security\np
 roofs.
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n\nAodhan Corrigan\n\nAFFILIATION:\n University of Wat
 erloo\n\nROOM:\n MC 5501\n\nABSTRACT: Quantum key distribution (QKD) prot
 ocols rely on the laws\nof physics for provably secure secret sharing\, bu
 t the laws of physics\nare notoriously tricky to harness. If the laser bei
 ng used for\nencoding is fluctuating in time\, how does this affect the se
 curity\nguarantees? In this talk\, I will cover the kinds of problems that
  can\narise in physical realizations of QKD protocols and the problems tha
 t\nthese might cause. After this\, I will give a (far from exhaustive)\nov
 erview of techniques that come up in dealing with such imperfections\nin t
 he implementation. This will be open-ended\, in the sense that\nquestions 
 that arise/different interests during the talk can dictate\nwhat we cover.
DTSTAMP:20261103T042629Z
END:VEVENT
BEGIN:VEVENT
UID:6ae96275b580e
DTSTART;TZID=America/Toronto:20261106T153000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261106T163000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/tutte-colloq
 uium-adam-van-tuyl-building-ideals-graphs-when
SUMMARY:Tutte Colloquium | Adam Van Tuyl\, Building ideals from graphs: whe
 n\nare they (geometrically) vertex decomposable?
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n Adam Van Tuyl\n\nAFFILIATION:\n McMaster University\
 n\nLOCATION:\n MC 5501\n\nABSTRACT: Vertex decomposable simplicial comple
 xes and geometrically\nvertex decomposable ideals have a lot of nice struc
 ture: they are\nshellable and Cohen–Macaulay\, and the ideal version is 
 also radical\nand glicci. There are many ways to attach an ideal to a grap
 h\, such as\nedge ideals\, toric ideals\, binomial edge ideals and star\nc
 onfigurations\, and the goal is to exploit the graph structure to\ndecide 
 whether the ideal is (geometrically) vertex decomposable. I\nwill introduc
 e these notions from scratch\, with no commutative algebra\nassumed\, and 
 survey recent joint work\, including a computer search of\nall graphs on 1
 1 vertices and a conjecture for binomial edge ideals.\n 
DTSTAMP:20261103T042629Z
END:VEVENT
BEGIN:VEVENT
UID:6ae96275b605f
DTSTART;TZID=America/Toronto:20261030T153000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261030T163000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/tutte-colloq
 uium-bertrand-guenin-integral-set-packing-versus
SUMMARY:Tutte Colloquium | Bertrand Guenin\, Integral Set Packing versus\nI
 ntegral Set Covering
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n Bertrand Guenin\n\nAFFILIATION:\n University of Wate
 rloo\n\nLOCATION:\n MC 5501\n\nABSTRACT: A 0-1 matrix M is _perfect_ if t
 he polyhedron {x ≥ 0 : Mx\n≤ 1} is integral. Perfect matrices are clos
 ely related to perfect\ngraphs and have several remarkable properties. In 
 particular\,\nperfectness is equivalent to total dual integrality\, and pe
 rfect\nmatrices admit an excluded-minor characterization.\n\nA 0-1 matrix 
 M is _ideal_ if the polyhedron {x ≥ 0 : Mx ≥ 1} is\nintegral. Unlike p
 erfect matrices\, ideal matrices do not correspond to\na single well-under
 stood class of combinatorial objects. In this talk\,\nwe will explore whic
 h of the remarkable properties of perfect matrices\nhave counterparts for 
 ideal matrices. We will discuss what is known\,\nwhat fails\, and some of 
 the intriguing open questions that arise from\nthis comparison.
DTSTAMP:20261103T042629Z
END:VEVENT
BEGIN:VEVENT
UID:6ae96275b6856
DTSTART;TZID=America/Toronto:20261026T110000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261026T120000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/combinatoric
 s-and-optimization-reading-group-arkaprava
SUMMARY:Combinatorics and Optimization reading group | Arkaprava Choudhury\
 ,\nProof of the Sunflower Conjecture
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n Arkaprava Choudhury\n\nAFFILIATION:\n University of 
 Waterloo\n\nROOM:\n MC 6029\n\nABSTRACT: A $k$-sunflower is a family of $
 k$ distinct sets whose\npairwise intersections all coincide. The Erd\\H{o}
 s--Szemer\\'edi\nconjecture asserts that for every $k \\ge 3$ there is a c
 onstant $c_k <\n2$ such that any $k$-sunflower-free family $\\mathcal{F} \
 \subseteq\n2^{[n]}$ satisfies $|\\mathcal{F}| \\le c_k^{\\\,n}$. Bucic\, H
 e\, and Lee\nrecently proved this with an explicit bound.\n\nIn this talk 
 we survey the problem and its place among sunflower\nquestions\, then work
  through the proof\, centered on a vector-sunflower\nargument. We also dis
 cuss how the result relates to a related problem\,\nthe uniform Erd\\H{o}s
 --Rado conjecture\, which it does not settle. No\nprior background is assu
 med. 
DTSTAMP:20261103T042629Z
END:VEVENT
BEGIN:VEVENT
UID:6ae96275b70ed
DTSTART;TZID=America/Toronto:20261026T150000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261026T160000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/graphs-and-m
 atroids-hidde-koerts-faster-3-colouring
SUMMARY:Graphs and Matroids | Hidde Koerts\, Faster 3-colouring algorithm f
 or\ngraphs of diameter 3
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n Hidde Koerts \n\nAFFILIATION:\n University of Water
 loo\n\nROOM:\n MC 6029\n\nABSTRACT: Determining whether a graph is k-colo
 urable is a famously\nhard computational problem. Even when placing signif
 icant restrictions\non the graph\, the resulting problem is often NP-hard.
  In this talk\,\nwe focus on the case of restricting the diameter. Under 
 the\nExponential Time Hypothesis\, there does not exist a sub-exponential\
 nalgorithm for 3-colouring diameter-4 graphs or for 4-colouring\ndiameter-
 2 graphs. Hence\, the interesting remaining cases are\n3-colouring graphs 
 of diameter 2 or 3. We show that 3-colouring\ndiameter-3 graphs can be so
 lved in 2^O(n^{2/3−ε}) for any ε < 1/33\nby providing an algorithm bas
 ed on a structural result. This improves\non the previous best known algor
 ithm due to Dębski\, Piecyk and\nRzążewski.\n\nThis talk is based on jo
 int work with Carla Groenland and Sophie\nSpirkl.
DTSTAMP:20261103T042629Z
END:VEVENT
BEGIN:VEVENT
UID:6ae96275b791d
DTSTART;TZID=America/Toronto:20261028T100000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261028T110000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/crypto-readi
 ng-group-quantum-computing-douglas-stebila-qkd
SUMMARY:Crypto Reading Group on quantum computing | Douglas Stebila\, QKD\n
 Security
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n Douglas Stebila\n\nAFFILIATION:\n University of Wate
 rloo\n\nROOM:\n MC 5501\n\nABSTRACT: Having seen the BB84 quantum key dis
 tribution protocol last\nweek\, this week we’ll see what it means for QK
 D to be secure\,\nfollowing the basic principle that “information gain i
 mplies\ndisturbance”. We’ll talk about what authentication is needed f
 or\nQKD’s security guarantees to hold\, and other factors like device\ns
 ecurity and finite key effects.
DTSTAMP:20261103T042629Z
END:VEVENT
BEGIN:VEVENT
UID:6ae96275b8257
DTSTART;TZID=America/Toronto:20261029T143000
SEQUENCE:0
TRANSP:TRANSPARENT
DTEND;TZID=America/Toronto:20261029T153000
URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-an
 d-enumerative-combinatorics-seminar-shao-yuan
SUMMARY:Algebraic and Enumerative Combinatorics Seminar | Shao Yuan Lin\,\n
 Distinguishability and linear independence for H-chromatic symmetric\nfunc
 tions
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n Shao Yuan Lin\n\nAFFILIATION:\n University of Waterl
 oo\n\nLOCATION:\n MC 5417\n\nABSTRACT: We study the H-chromatic symmetric
  functions X_G^H\nintroduced by Eagles et al. (2022)\, which generalizes t
 he chromatic\nsymmetric function X_G to the context of H-colorings\, which
  tracks\ngraph homomorphisms G → H. We first show that self-chromatic\ns
 ymmetric functions X_G^G determine quantities like the connected\ncomponen
 ts of a forest and the degree sequence of a caterpillar. We\nthen show tha
 t the X_G^H's form a basis of the symmetric function ring\nfor certain col
 lections of (G\,H)\, such as the self-CSFs of complete\nmultipartite graph
 s. Lastly\, we define and discuss H-chromatic\npolynomials as specializati
 ons of H-CSFs. This is joint work with\nLaura Pierson.\n\nThere will be a 
 pre-seminar presenting relevant background at\nbeginning graduate level st
 arting at 1:30pm in MC 5417.
DTSTAMP:20261103T042629Z
END:VEVENT
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