Colloquia & Seminars Archives - Page 120 of 130

Seminars: Colloquia & Seminars

Date
Time
Venue

Speaker
Affiliation
Title of Talk

02 Oct 2019
10:00
S16 #03-09

Bao Huanchen
National University of Singapore
The m=2 amplituhedron

The m=2 amplituhedron

Date/Time : 02 Oct 2019 10:00
Venue : S16 #03-09
Speaker : Bao Huanchen, National University of Singapore

Date/Time:02 Oct 2019 10:00 Venue: S16 #03-09 Speaker: Bao Huanchen, National University of Singapore The m=2 amplituhedron An amplituhedron (defined in terms of totally nonnegative Grassmannians) is a geometric structure introduced in 2013 by two physicists Nima Arkani-Hamed and Jaroslav Trnka. In this talk I shall explain the triangulation of the m=2 amplituhedron. This is joint work with Xuhua He. Add to calendar:

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02 Oct 2019
16:00
S17 #05-11 SR5

SHAO Sihong
Peking University
Lovász extension and graph cut

Lovász extension and graph cut

Date/Time : 02 Oct 2019 16:00
Venue : S17 #05-11 SR5
Speaker : SHAO Sihong, Peking University

Date/Time:02 Oct 2019 16:00 Venue: S17 #05-11 SR5 Speaker: SHAO Sihong, Peking University Lovász extension and graph cut A firm bridge between discrete data world and continuous math field should be tremendously helpful in data analysis. Along this direction, the Lovász extension provides a both explicit and equivalent continuous optimization problem for a discrete optimization problem, for instance, the Cheeger cut problem. In this talk, we report a set- pair Lovász extension which provides not only an answer to the dual Cheeger cut, anti-Cheeger cut, and max 3-cut problems, all of which cannot be handled by the Lovász extension, but also works for the Cheeger cut and maxcut problems. In particular, the set-pair Lovász extension enlarges the feasible region of resulting equivalent continuous optimization problems from a half space (resulted from the Lovász extension ) to the entire space for the Cheeger cut and maxcut problems. On the other hand, it provides new possibilities for designing continuous optimization algorithms for combination problems on the practical side, too. As an illustration, we propose a simple continuous iterative algorithm for the maxcut problem which converges to a local optimum in finite steps. Here ‘simple’ means the inner subproblem is solved analytically and thus no optimization solver is called. Preliminary results on G-set demonstrate that the ratio between the best cut values achieved by the simple algorithm without any local breakout techniques and the best known ones is of at least $0.986$. Add to calendar:

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02 Oct 2019
16:00
S16 #03-09

Yin Silu
Hangzhou Normal University
Global well-posedness of elastodynamics

Global well-posedness of elastodynamics

Date/Time : 02 Oct 2019 16:00
Venue : S16 #03-09
Speaker : Yin Silu, Hangzhou Normal University

Date/Time:02 Oct 2019 16:00 Venue: S16 #03-09 Speaker: Yin Silu, Hangzhou Normal University Global well-posedness of elastodynamics In this talk, I will present some classical theory of elastic waves. The motion of elasticity is a wave system with multiple speeds, so Lorentz invariant is absent. For incompressible isotropic elasticity with constant density in 3D, the Cauchy problem with small initial datum were studied by a series work of Sideris and Thomases. We studied the inhomogeneous case in Lagrangian coordinate under the assumption that the density is a small perturbation around a constant state. This is a joint work with Xiufang Cui. Add to calendar:

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25 Sep 2019
10:00
S16 #03-09

Max Gurevich
National University of Singapore
Robinson-Schensted-Knuth correspondence at the service of p-adic GL(n)

Robinson-Schensted-Knuth correspondence at the service of p-adic GL(n)

Date/Time : 25 Sep 2019 10:00
Venue : S16 #03-09
Speaker : Max Gurevich, National University of Singapore

Date/Time:25 Sep 2019 10:00 Venue: S16 #03-09 Speaker: Max Gurevich, National University of Singapore Robinson-Schensted-Knuth correspondence at the service of p-adic GL(n) In a joint work with Erez Lapid we constructed a new class of representations based on applying the RSK algorithm on Zelevinski’s multisegments. Those constructions have the potential to be an alternative to the commonly used basis of standard representations. Intriguingly, this class also turned out to categorify a 45-year-old development in invariant theory: The Rota basis of standard bitableaux. I will talk about this classical theme and its relation to representations of p-adic GL(n), as well the expected properties of our new class. Add to calendar:

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25 Sep 2019
16:00
S17 #06-11

Foo Wei Guo
Chinese Academy of Sciences
Equivalence problem of CR real hypersurfaces with uniform Levi rank: the degenerate case

Equivalence problem of CR real hypersurfaces with uniform Levi rank: the degenerate case

Date/Time : 25 Sep 2019 16:00
Venue : S17 #06-11
Speaker : Foo Wei Guo , Chinese Academy of Sciences

Date/Time:25 Sep 2019 16:00 Venue: S17 #06-11 Speaker: Foo Wei Guo, Chinese Academy of Sciences Equivalence problem of CR real hypersurfaces with uniform Levi rank: the degenerate case In this talk, we discuss about the Cartan’s equivalence problem of 5-dimensional CR real hypersurfaces of constant Levi rank 1, and which are 2-non-degenerate. An important homogeneous model is the tube over the future light cone which has 10 dimensional Lie algebra of infinitesimal CR automorphisms, isomorphic to so(3,2). In 2015, Samuel Pocchiola in his joint work with Joel Merker produced 2 primary invariants which characterise such a homogeneous model. If time permits, we might discuss about the geometry of PDE for this problem which has relation to third order ODE and the Einstein-Weyl geometry. Add to calendar:

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18 Sep 2019
16:00
S16 #03-09

Chen Haoyang
Fudan University
Global regularity for Einstein-Klein-Gordon system with $U(1) \times \mathbb{R}$ isometry group

Global regularity for Einstein-Klein-Gordon system with $U(1) \times \mathbb{R}$ isometry group

Date/Time : 18 Sep 2019 16:00
Venue : S16 #03-09
Speaker : Chen Haoyang, Fudan University

Date/Time:18 Sep 2019 16:00 Venue: S16 #03-09 Speaker: Chen Haoyang, Fudan University Global regularity for Einstein-Klein-Gordon system with $U(1) \times \mathbb{R}$ isometry group In this paper we prove the global regularity of the 3+1 dimensional Einstein-Klein-Gordon system with a $U(1)\times \mathbb{R}$ isometry group. We reduce the Cauchy problem of the Einstein-Klein-Gordon system to a 2+1 dimensional system. We prove that the energy of this system cannot concentrate near the first possible singularity, and hence is small. Then, we show that the global regularity holds for the reduced 2+1 dimensional system with initial data of small energy. Add to calendar:

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18 Sep 2019
10:00
S16 #03-09

Bao Huanchen
National University of Singapore
Total positivity in reductive groups II

Total positivity in reductive groups II

Date/Time : 18 Sep 2019 10:00
Venue : S16 #03-09
Speaker : Bao Huanchen, National University of Singapore

Date/Time:18 Sep 2019 10:00 Venue: S16 #03-09 Speaker: Bao Huanchen, National University of Singapore Total positivity in reductive groups II I will explain the cellular decompositions of totally nonnegative flag variety and totally nonnegative springer fibres. The references are the following: K. Rietsch, “An algebraic cell decomposition of the nonnegative part of a flag variety”; R. Marsh and K. Rietsch, “Parametrizations of flag varieties’’; G. Lusztig, “Total positivity in Springer fibres”. Add to calendar:

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12 Sep 2019
17:00
S17 #06-11

Gao Ziyuan
National University of Singapore
The one-cop-moves game on planar graphs

The one-cop-moves game on planar graphs

Date/Time : 12 Sep 2019 17:00
Venue : S17 #06-11
Speaker : Gao Ziyuan, National University of Singapore

Date/Time:12 Sep 2019 17:00 Venue: S17 #06-11 Speaker: Gao Ziyuan, National University of Singapore The one-cop-moves game on planar graphs Cops and Robbers is a vertex-pursuit game played on graphs. In this game, a set of cops and a robber occupy the vertices of the graph and move alternately along the graph’s edges with perfect information about each other’ positions. If a cop eventually occupies the same vertex as the robber, then the cops win; the robber wins if she can indefinitely evade capture. Aigner and Fromme established that in every connected planar graph, three cops are sufficient to capture a single robber. In this paper, we consider a recently studied variant of the cops and robbers game, alternately called the one-active-cop game, one-cop-moves game or the lazy cops and robbers game, where at most one cop can move during any round. We show that Aigner and Fromme’s result does not generalize to this game variant by constructing a connected planar graph on which a robber can indefinitely evade three cops in the one-cop-moves game. This talk is based on joint work with Boting Yang (http://www2.cs.uregina.ca/~boting/). Add to calendar:

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11 Sep 2019
16:00
S17 #05-11 SR5

Krishna Balasubramanian
UC Davis
Applications of Gaussian Stein’s Identity to Non-Convex Optimization and Sampling

Applications of Gaussian Stein’s Identity to Non-Convex Optimization and Sampling

Date/Time : 11 Sep 2019 16:00
Venue : S17 #05-11 SR5
Speaker : Krishna Balasubramanian, UC Davis

Date/Time:11 Sep 2019 16:00 Venue: S17 #05-11 SR5 Speaker: Krishna Balasubramanian, UC Davis Applications of Gaussian Stein’s Identity to Non-Convex Optimization and Sampling Optimization and sampling are arguably the computational backbones of Frequentist and Bayesian statistics respectively. In this talk the use of Gaussian Stein’s identity for performing stochastic Zeroth-Order (ZO) non-convex optimization and sampling will be discussed. Specifically, we consider the case when the function (or density) under consideration is not available to us analytically, rather we are able to only obtain noisy evaluations. Using Gaussian Stein’s identity, techniques for estimating the gradient and Hessian of a function (or density) will be introduced. Based on this, the following algorithms and the corresponding theoretical results will be discussed: (i) ZO stochastic gradient method in high-dimensions (ii) ZO Newton’s method for escaping saddle points (iii) ZO Euler and Ozaki discretized (Kinetic) Langevin Monte Carlo sampling. Add to calendar:

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