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:68aaf0b37d892 DTSTART;TZID=America/Toronto:20250819T153000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20250819T163000 URL:/combinatorics-and-optimization/events/tutte-colloq uium-niv-buchbinder SUMMARY:Tutte Colloquium - Niv Buchbinder CLASS:PUBLIC DESCRIPTION:Summary \n\nTITLE: Deterministic Algorithms and Faster Algorit hms for Submodular\nMaximization subject to a Matroid Constraint\n\nSPEAKE R:\n Niv Buchbinder\n\nAFFILIATION:\n Statistics and Operations Research a t Tel Aviv university\n\nLOCATION:\n MC 5501\n\nABSTRACT: Maximization of submodular functions under various\nconstraints is a fundamental problem that has been studied\nextensively.\n\nIn this talk I will discuss submodu lar functions and interesting\nresearch questions in the field.\n\nI will present several new techniques that lead to both deterministic\nalgorithms and faster randomized algorithms for maximizing submodular\nfunctions.\n\ nIn particular\, for monotone submodular functions subject to a matroid\nc onstraint we design a deterministic non-oblivious local search\nalgorithm that has an approximation guarantee of 1 - 1/e - \\eps (for\nany \\eps > 0 )\, vastly improving over the previous state-of-the-art\n0.5008-approximat ion.\n\nFor general (non-monotone) submodular functions we introduce a new \ntool\, that we refer to as the extended multilinear extension\, designed \nto derandomize submodular maximization algorithms that are based on\nthe successful ``solve fractionally and then round'' approach.\n\nSHORT BIO: Niv Buchbinder is a professor in the department of\nStatistics and Operati ons Research at Tel Aviv university. He\nreceived his Ph.D. in Computer S cience from the Technion\, Israel in\n2008\, and then spent two years as a post-doctoral researcher at\nMicrosoft Research\, New England\, MA. His p rimary research interests\nare algorithms for combinatorial optimization p roblems in offline and\nonline settings.\n DTSTAMP:20250824T110003Z END:VEVENT BEGIN:VEVENT UID:68aaf0b37fee6 DTSTART;TZID=America/Toronto:20250805T143000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20250805T153000 URL:/combinatorics-and-optimization/events/graphs-and-m atroids-richard-peng-cmu SUMMARY:Graphs and Matroids - Richard Peng (CMU) CLASS:PUBLIC DESCRIPTION:Summary \n\nTITLE: Approximating Distances on Undirected Graph s\n\nSPEAKER:\n Richard Peng \n\nAFFILIATION:\n Carnegie Mellon Universit y\n\nROOM:\n MC 5501\n\nABSTRACT: The shortest path metric on undirected graphs is a\nfundamental quantity with deep connections to combinatorics a nd\nstructural graph theory. Tools built around such approximations are\np laying increasingly important role in efficient optimization\nalgorithms a nd data structures. This talk will introduce such\napproximations starting from the breadth first search tree\, and build\nupon them to discuss dist ance oracles and oblivious routings.\n DTSTAMP:20250824T110003Z END:VEVENT BEGIN:VEVENT UID:68aaf0b3807e1 DTSTART;TZID=America/Toronto:20250807T143000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20250807T153000 URL:/combinatorics-and-optimization/events/algebraic-an d-enumerative-combinatorics-seminar-tia-ruza SUMMARY:Algebraic and enumerative combinatorics seminar-Tia Ruza CLASS:PUBLIC DESCRIPTION:Summary \n\nTITLE: Multivariate Limit Theorems and Algebraic Ge nerating Functions\n\nSpeaker\n\nTia Ruza\n\nAffiliation\n University of W aterloo\n\nLocation\n MC 5479\n\nABSTRACT: The field of analytic combinato rics in several variables\n\n(ACSV) is dedicated to the creation of effect ive techniques to study\nthe large-scale behaviour of combinatorial object s. This talk provides\nresults for two areas of ACSV: limit theorems and a symptotics of\nalgebraic generating functions. First\, I will describe an automated\napproach to proving local central limit theorems and its applic ations\nto a variety of examples. Included in these examples will be a fam ily\nof permutations with restricted cycles\, integer compositions with\nt racked summands and n-colour compositions with tracked summands. The\nseco nd half of the talk will survey techniques for analyzing\nmultivariate alg ebraic generating functions\, going into detail\nspecifically for the proc ess of embedding an algebraic generating\nfunction into a sub-series of a rational function of more variables.\nFor both parts of the talk\, SageMat h code which automates the methods\ndiscussed will be demonstrated for var ious examples.\n\nTHERE WILL BE A PRE-SEMINAR PRESENTING RELEVANT BACKGROU ND AT THE\nBEGINNING GRADUATE LEVEL STARTING AT 1:30PM.\n DTSTAMP:20250824T110003Z END:VEVENT BEGIN:VEVENT UID:68aaf0b3810e8 DTSTART;TZID=America/Toronto:20250731T133000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20250731T153000 URL:/combinatorics-and-optimization/events/algebraic-an d-enumerative-combinatorics-seminar-ura-day-kai SUMMARY:Algebraic and enumerative combinatorics seminar-URA day! Kai Choi\, \nPeiran Tao\, Stephanie Penner CLASS:PUBLIC DESCRIPTION:Summary \n\nSpeaker\n\nURA day!  Kai Choi\, Peiran Tao\, Steph anie Penner\n\nAffiliation\n University of À¶Ý®ÊÓƵ\n\nLocation\n MC 5479\ n\nKai Choi\n\nTITLE:Alice in Quadraticspanningforestidentityspace\n\nABST RACT: Quantum field theorists study Feynman periods\, which are\nobtained by integrating expressions related to the spanning tree\npolynomials of g raphs known as Feynman diagrams. But if you are like\nme and know nothing about physics\, the good news is that doing quantum\nfield theory often le ads one to play with combinatorial objects. In\nparticular\, if one wishes to efficiently compute Feynman periods\, they\nwould likely be faced with unanswered questions about set partitions\,\ndeterminantal identities\, s paces of polynomials\, and the all-minors\nmatrix-tree theorem\, many of w hich are quite accessible. I will\npresent these questions and their relev ant background in the context\nof my work on spaces of quadratic spanning forest identities\,\nsupervised by Dr. Karen Yeats.\n\nPeiran Tao\n\nTITLE :Alice in Quadraticspanningforestidentityspace\n\nABSTRACT: It is a class ical theorem that the diagonal of any\nbivariate rational power series is algebraic\; that is\, it satisfies a\npolynomial equation. We will discuss an algorithm that efficiently\ncomputes this polynomial.\n\nGiven a ratio nal generating function F(z_1\,...\,z_d) we are interested\nin the asympto tic behaviour of its coefficient sequence in a specified\ndirection (r_1\, ...\,r_d). Although this problem is difficult in\ngeneral\, when d=2 and w hen some conditions are satisfied\, there is a\nknown algorithm that resol ves it. We will explain the basics of\nanalytic combinatorics in several v ariables and show how this\nalgorithm operates.\n\nStephanie Penner\n\nTIT LE: Combinatorial Exploration: Counting Chord Diagrams\n\nABSTRACT: It can often be tricky to find a combinatorial specification\nof a counting sequ ence for a given set of objects. A recently\ndeveloped framework called \" Combinatorial Exploration\" aims to\nautomate the process of finding combi natorial specifications. It has\nsuccessfully been used to find specificat ions for several new\npermutation classes and looks promising for several other objects. In\nthis talk\, I will briefly explain how Combinatorial Ex ploration works\,\nand how I am using it to automate finding specification s for families\nchord diagrams.\n DTSTAMP:20250824T110003Z END:VEVENT BEGIN:VEVENT UID:68aaf0b381c3a DTSTART;TZID=America/Toronto:20250722T143000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20250722T153000 URL:/combinatorics-and-optimization/events/graphs-and-m atroids-nathan-bowler SUMMARY:Graphs and Matroids - Nathan Bowler CLASS:PUBLIC DESCRIPTION:Summary \n\nTITLE: Circuit partitions of finitary binary matro ids\n\nSPEAKER:\n Nathan Bowler\n\nAFFILIATION:\n University of Hamburg\n \nROOM:\n MC 6483\n\nABSTRACT: Nash-Williams showed in 1960 that a (possi bly infinite)\ngraph can be expressed as a union of edge-disjoint cycles i f and only\nif it has no odd cut. Recently\, Joó extended this result to directed\ngraphs\, showing that a directed graph can be expressed as a uni on of\nedge-disjoint directed cycles if and only if every cut contains the \nsame number of edges in each direction. We extend these results to\nfini tary binary matroids. This is joint work with Attila Joó.\n DTSTAMP:20250824T110003Z END:VEVENT BEGIN:VEVENT UID:68aaf0b382554 DTSTART;TZID=America/Toronto:20250725T153000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20250725T163000 URL:/combinatorics-and-optimization/events/tutte-colloq uium-samuel-jaques-0 SUMMARY:Tutte Colloquium - Samuel Jaques CLASS:PUBLIC DESCRIPTION:Summary \n\nTITLE: The Landscape of Quantum Computing\n\nSPEAK ER:\n Samuel Jaques\n\nAFFILIATION:\n University of À¶Ý®ÊÓƵ\n\nLOCATION:\ n MC 5501\n\nABSTRACT: Quantum computers will be able to break all the\nc ryptography we have relied on for the last 4 decades\, but when will\nthey have this power? In this talk I will give a high-level overview\nof where quantum computing technologies are today\, the path they will\nneed to ta ke\, and what kind of discoveries could help or hinder\nprogress in quantu m computing.\n DTSTAMP:20250824T110003Z END:VEVENT BEGIN:VEVENT UID:68aaf0b382eea DTSTART;TZID=America/Toronto:20250717T130000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20250717T143000 URL:/combinatorics-and-optimization/events/co-reading-g roup-rian-neogi-9 SUMMARY:C&O Reading Group -Rian Neogi CLASS:PUBLIC DESCRIPTION:Summary \n\nTITLE: : Optimal Item Pricing in Online Combinator ial Auctions\n\nSPEAKER:\n Rian Neogi\n\nAFFILIATION:\n University of Wate rloo\n\nLOCATION:\n MC 6029\n\nABSTRACT: I will present a paper by Correa \, Cristi\, Fielbaum\,\nPollner\, and Weinberg. The paper studies the onli ne combinatorial\nauction problem when buyers are interested in sets of si ze at most d.\nThey show that there exist item prices such that the posted price\nmechanism under these prices results in an allocation that is\n(d+ 1)-approximate with respect to the offline benchmark. They show the\nexist ence of these prices through a novel use of Brouwer's fixed point\ntheorem .\n DTSTAMP:20250824T110003Z END:VEVENT BEGIN:VEVENT UID:68aaf0b3837a7 DTSTART;TZID=America/Toronto:20250718T153000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20250718T163000 URL:/combinatorics-and-optimization/events/tutte-colloq uium-ashwin-nayak-1 SUMMARY:Tutte colloquium-Ashwin Nayak CLASS:PUBLIC DESCRIPTION:Summary \n\nTITLE:Learning quantum states\n\nSPEAKER:\n Ashwin Nayak\n\nAFFILIATION:\n University of À¶Ý®ÊÓƵ\n\nLOCATION:\n MC 5501\n\nA BSTRACT: Suppose we are given a sequence of quantum registers\ninitialize d to the same quantum state rho\, and would like to learn\nthe state rho. That is\, we would like to design an algorithm that\nproduces a classica l description of an approximation to the state.\nHow many copies of rho d owe need to be able to produce a suitable\napproximation? This talk will  be a gentle introduction to the problem\nand related results.\n\n \n DTSTAMP:20250824T110003Z END:VEVENT BEGIN:VEVENT UID:68aaf0b384303 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:20250824T110003Z END:VEVENT BEGIN:VEVENT UID:68aaf0b384dd8 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:20250824T110003Z END:VEVENT END:VCALENDAR