Print Friendly printer friendly
 Events
Idaho
Mon 20 Nov 2017, 4:00pm
Algebraic Geometry Seminar
MATH 126
Equations for surfaces in projective four-space
MATH 126
Mon 20 Nov 2017, 4:00pm-5:00pm

Abstract

This talk is concerned with the question of the minimal number of equations necessary to define a given projective variety scheme-theoretically. Every hypersurface is cut out by a single polynomial scheme-theoretically (also set-theoretically and ideal theoretically).  Therefore the question is more interesting if a variety has a higher codimension. In this talk, we focus on the case when the codimension is two. If a variety in projective n-space has codimension two, then the minimal number of polynomials necessary to cut out the variety scheme-theoretically is between 2 and n+1. However the varieties cut out by fewer than n+1, but more than 2 polynomials seem very rare. The main goal of this talk is to discuss conditions for a non-singular surface in projective four-space to be cut out by three polynomials. 
hide
Mike Irvine
Institute of Applied Mathematics, UBC
Tue 21 Nov 2017, 12:30pm
Scientific Computation and Applied & Industrial Mathematics
ESB 4133 (PIMS Lounge)
Likelihood-free methods: Challenges in fitting individual-based models to epidemiological data
ESB 4133 (PIMS Lounge)
Tue 21 Nov 2017, 12:30pm-1:30pm

Abstract

Complex individual-based models abound in epidemiology and ecology. Fitting these models to data is a challenging problem: methodologies can be inaccessible to all but specialists, there may be challenges in adequately describing uncertainty in model fitting, and the complex models may take a long time to run, requiring parameter selection procedures. Approximate Bayesian Computation has been proposed as a likelihood-free method in resolving these issues, however requires careful selection of summary statistics and annealing scheme. I compare this procedure directly to standard methodologies where the likelihood exists, Markov-chain Monte Carlo and maximum likelihood. This is then applied to a complex individual-based simulation for lymphatic filariasis, a human parasitic disease, which affects over 120 million individuals internationally. Finally, I will discuss a new approach to individual-based model fitting by constructing a synthetic likelihood using mixture density networks. 
hide
Michal Kowalczyk
University of Chile
Tue 21 Nov 2017, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
ESB 2012
Asymptotic stability for some nonlinear Klein-Gordon equations for odd perturbations in the energy space
ESB 2012
Tue 21 Nov 2017, 3:30pm-4:30pm

Abstract

 Showing asymptotic stability in one dimensional nonlinear Klein-Gordon equations is a notoriously difficult problem. In this talk I will describe an approach based on virial estimates which allows to prove it in case when only odd perturbations are allowed. In particular I will discuss asymptotic stability of the kink in the \phi^4 model.       
hide
Brown University
Tue 21 Nov 2017, 4:00pm SPECIAL
Algebraic Geometry Seminar
MATH 126
The Picard group of the moduli of smooth complete intersections of two quadrics
MATH 126
Tue 21 Nov 2017, 4:00pm-5:00pm

Abstract

 We study the moduli space of smooth complete intersections of two quadrics by relating it to the geometry of the singular members of the corresponding pencil. We give a new description for this parameter space by using the fact that two quadrics can be simultaneously diagonalized. Using this description we can compute the Picard group, which always happens to be cyclic. For example, we show that the Picard group of the moduli stack of smooth degree 4 Del Pezzo surfaces is Z/4Z. 

This is a joint work with Giovanni Inchiostro.

hide
UBC, Math
Wed 22 Nov 2017, 2:00pm
Mathematical Biology Seminar
PIMS (ESB 4th floor)
Pattern formation on a Slowly Flattening Spherical Cap: A closest Point Method Approach.
PIMS (ESB 4th floor)
Wed 22 Nov 2017, 2:00pm-3:00pm

Abstract


hide
UBC
Wed 22 Nov 2017, 3:00pm
Probability Seminar
ESB 2012
Spin systems and some natural questions in probability
ESB 2012
Wed 22 Nov 2017, 3:00pm-4:00pm

Abstract

 
It has long been known that many interesting questions in probability have a formulation in the language of spin systems. However, it has been only rather recently that the methods developed for spin systems were applied to finally obtain answers to some of these questions. In this talk, I will discuss three such questions, about the weakly self-avoiding walk, the vertex reinforced jump process, and random band matrices. I will then show the audience some technical lemmas that are at the heart of the analysis of spin systems.
hide
UBC
Wed 22 Nov 2017, 3:15pm
Topology and related seminars
ESB 4133 (PIMS Lounge)
The A1 calculation of the 4th homotopy group of the 6,3-sphere and a conjecture of Suslin.
ESB 4133 (PIMS Lounge)
Wed 22 Nov 2017, 3:15pm-4:15pm

Abstract

 The algebraic K-theory, due to Quillen, of a field is related to a theory defined by Milnor called Milnor K-theory and denoted K^M. In the 1980s, Andrei Suslin constructed a map K_n(F) -> K^M_n(F), and conjectured that the image was the subgroup (n-1)! K^M_n(F). He also proved the conjecture for n<=3. For n=5, we reinterpret the construction as a construction in the A1 homotopy groups of spheres and BGL, and by calculating these groups, show that the conjecture is true in this case as well. This represents part of a joint project with Aravind Asok,  Jean Fasel and Kirsten Wickelgren.
hide
Texas A&M
Thu 23 Nov 2017, 4:00pm SPECIAL
Algebraic Geometry Seminar
MATX 1102
Irrational Toric Varieties
MATX 1102
Thu 23 Nov 2017, 4:00pm-5:00pm

Abstract

Classical toric varieties come in two flavours: Normal toric varieties are given by rational fans in R^n. A (not necessarily normal) affine toric variety is given by finite subset A of Z^n. When A is homogeneous, it is projective. Applications of mathematics have long studied the positive real part of a toric variety as the main object, where the points A may be arbitrary points in R^n. For example, in 1963 Birch showed that such an irrational toric variety is homeomorphic to the convex hull of the set A.

Recent work showing that all Hausdorff limits of translates of irrational toric varieties are toric degenerations suggested the need for a theory of irrational toric varieties associated to arbitrary fans in R^n. These are R^n_>-equivariant cell complexes dual to the fan. Among the pleasing parallels with the classical theory is that the space of Hausdorff limits of the irrational projective toric variety of a finite set A in R^n is homeomorphic to the secondary polytope of A.

hide
Columbia
Mon 27 Nov 2017, 4:00pm
Algebraic Geometry Seminar
MATH 126
Arithmetic representations of fundamental groups
MATH 126
Mon 27 Nov 2017, 4:00pm-5:00pm

Abstract

 Let X be an algebraic variety over a field k. Which representations of pi_1(X) arise from geometry, e.g. as monodromy representations on the cohomology of a family of varieties over X? We study this question by analyzing the action of the Galois group of k on the fundamental group of X, and prove several fundamental structural results about this action.

As a sample application of our techniques, we show that if X is a normal variety over a field of characteristic zero, and p is a prime, then there exists an integer N=N(X,p) such that any non-trivial p-adic representation of the fundamental group of X, which arises from geometry, is non-trivial mod p^N.

hide
Wed 29 Nov 2017, 2:45pm SPECIAL
ESB 4133 (PIMS Lounge)
Nov. 29th PIMS Afternoon Tea has been moved to 4:30pm-5:00pm
ESB 4133 (PIMS Lounge)
Wed 29 Nov 2017, 2:45pm-3:15pm

Details

The last PIMS Afternoon Tea of the fall semester will take place before Marco Cuturi's 5:00 pm PIMS Distinguished Colloquium.
hide
Columbia
Wed 29 Nov 2017, 4:00pm
Algebraic Geometry Seminar
MATH 126
TBA
MATH 126
Wed 29 Nov 2017, 4:00pm-5:00pm

Abstract

 TBA
hide
Université Paris-Saclay
Wed 29 Nov 2017, 5:00pm SPECIAL
Department Colloquium
ESB 2012
PIMS Distinguished Colloquium: Generative Models and Optimal Transport
ESB 2012
Wed 29 Nov 2017, 5:00pm-6:00pm

Abstract

A recent wave of contributions in machine learning center on the concept of generative models for extremely complex data such as natural images. These approaches provide principled ways to use deep network architectures, large datasets and automatic differentiation to come up with algorithms that are able to synthesize realistic images. We will present in this talk how optimal transport is gradually establishing itself as a valuable tool to carry out this estimation procedure.

Note for Attendees

The last PIMS Afternoon Tea/Reception of the fall semester will take place from 4:30pm - 5:00pm in the PIMS Lounge.


This Colloquium is a series of talks at UBC by Marco Cuturi. He will be giving two other lectures on Thursday, Nov 30 and Friday Dec 1, 2017. 
hide
Université Paris-Saclay
Thu 30 Nov 2017, 5:00pm SPECIAL
ESB 2012
UBC Mathematics Lecture Series:: Regularized Optimal Transport. Part I.
ESB 2012
Thu 30 Nov 2017, 5:00pm-6:30pm

Details

 Optimal transport theory provides practitioners from statistics, imaging, graphics or machine learning with a very powerful toolbox to compare probability measures. These tools translate however in their original form into computational schemes that can become intractable or suffer from instability (such as non-differentiability or estimation bias). We will present in these two lectures how a few insights from optimization theory and in particular a careful regularization can result in tools that are considerably easier to implement, run faster because they can take advantage of parallel hardware and behave better from a statistical perspective. We will highlight applications from diverse areas, from graphics and brain imaging to text analysis and parametric estimation.

Note for Attendees

 This is the first of a two part lecture. The second part will be given on Dec, 1 2017, in ESB 2012 at the same time. Details for Part II are available here
hide
Courant Institute, NYU
Fri 1 Dec 2017, 3:00pm SPECIAL
Department Colloquium
ESB 2012
PIMS-UBC Distinguished Colloquium--Microscopic description of Coulomb-type systems
ESB 2012
Fri 1 Dec 2017, 3:00pm-4:00pm

Abstract

 
 

Systems of points with Coulomb, logarithmic (or more generally inverse powers of the distance) interactions arise in various settings: an instance is the classical Coulomb gas which in some cases happens to be a random matrix ensemble, another is vortices in the Ginzburg-Landau model of superconductivity, where one observes in certain regimes the emergence of densely packed point vortices forming perfect triangular lattice patterns named Abrikosov lattices, a third is the study of Fekete points which arise in approximation theory. After reviewing the motivations, we will take a point of view based on the detailed expansion of the interaction energy to describe the microscopic behavior of the systems and its statistical mechanics. In particular a Central Limit Theorem for fluctuations and a Large Deviations Principle for the microscopic point processes are given. This allows to observe the effect of the temperature as it gets very large or very small, and to connect with crystallization questions.

The main results are joint with Thomas Leblé and also based on previous works with Etienne Sandier, Nicolas Rougerie and Mircea Petrache.

Note for Attendees

Light refreshments will be served at 2:45pm in ESB 4133, the PIMS Lounge before this colloquium.
hide
Université Paris-Saclay
Fri 1 Dec 2017, 5:00pm SPECIAL
ESB 2012
UBC Mathematics Lecture Series: Regularized Optimal Transport. Part II
ESB 2012
Fri 1 Dec 2017, 5:00pm-6:30pm

Details

 Optimal transport theory provides practitioners from statistics, imaging, graphics or machine learning with a very powerful toolbox to compare probability measures. These tools translate however in their original form into computational schemes that can become intractable or suffer from instability (such as non-differentiability or estimation bias). We will present in these two lectures how a few insights from optimization theory and in particular a careful regularization can result in tools that are considerably easier to implement, run faster because they can take advantage of parallel hardware and behave better from a statistical perspective. We will highlight applications from diverse areas, from graphics and brain imaging to text analysis and parametric estimation.

Note for Attendees

 This is the second of a two part lecture. The first part will be given on Nov 30 2017, in ESB 2012 at the same time. Details for Part I are available here.
hide
University of Lethbridge
Thu 4 Jan 2018, 3:30pm
Number Theory Seminar
TBA
TBA
TBA
Thu 4 Jan 2018, 3:30pm-10:00am

Abstract


hide
University of Toronto
Thu 4 Jan 2018, 3:30pm SPECIAL
Diff. Geom, Math. Phys., PDE Seminar
TBA
TBA
TBA
Thu 4 Jan 2018, 3:30pm-5:00pm

Abstract

 
hide
Kevin Luli
UC-Davies
Tue 9 Jan 2018, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
ESB 2012
Variational Problems on Arbitrary Sets
ESB 2012
Tue 9 Jan 2018, 3:30pm-4:30pm

Abstract

 : Let E be an arbitrary subset of R^n. Given real valued functions f defined on E and g defined on R^n, the classical obstacle problem asks for a minimizer of the Dirichlet energy subject to the following two constraints: (1) F = f on E and (2) F lies above g on R^n. In this talk, we will discuss how to use extension theory to construct (almost) solutions directly. We will also explain several recent results that will help lay the foundation for building a complete theory revolving around the belief that any variational problems that can be solved using PDE theory can also be dealt with using extension theory.
hide
Harvard
Thu 25 Jan 2018, 4:00pm SPECIAL
TBA
TBA
TBA
Thu 25 Jan 2018, 4:00pm-5:00pm

Details


hide
Umberto Zannier
SNS, Pisa
Fri 2 Mar 2018, 3:00pm SPECIAL
Department Colloquium
ESB2012
PIMS-UBC Distinguished Colloquium--TBA
ESB2012
Fri 2 Mar 2018, 3:00pm-4:00pm

Abstract

 

Note for Attendees

Refreshments will be served in ESB 4133 from 2:45 p.m.-3:00 p.m.
hide
TBA
UBC Math
Fri 9 Mar 2018, 3:00pm
Department Colloquium
ESB 2012
Graduate Research Award: TBA
ESB 2012
Fri 9 Mar 2018, 3:00pm-4:00pm

Abstract


hide
TBA
UBC Math
Fri 16 Mar 2018, 3:00pm
Department Colloquium
ESB 2012
Graduate Research Award: TBA
ESB 2012
Fri 16 Mar 2018, 3:00pm-4:00pm

Abstract


hide
Oregon
Mon 19 Mar 2018, 4:00pm
Algebraic Geometry Seminar
MATH 126
TBA
MATH 126
Mon 19 Mar 2018, 4:00pm-5:00pm

Abstract

 TBA
hide
TBA
UBC Math
Fri 23 Mar 2018, 3:00pm
Department Colloquium
ESB 2012
Graduate Research Award: TBA
ESB 2012
Fri 23 Mar 2018, 3:00pm-4:00pm

Abstract


hide
MIT
Tue 27 Mar 2018, 4:00pm
Discrete Math Seminar
ESB 4127
TBD
ESB 4127
Tue 27 Mar 2018, 4:00pm-5:00pm

Abstract

 
hide
Jean-Marc Deshouillers
University of Bordeaux
Thu 29 Mar 2018, 3:30pm
Number Theory Seminar
TBA
Thu 29 Mar 2018, 3:30pm-5:00pm

Abstract


hide
University of Oxford
Fri 6 Apr 2018, 3:00pm
Department Colloquium
ESB 2012
PIMS-UBC Distinguished Colloquium--TBA
ESB 2012
Fri 6 Apr 2018, 3:00pm-4:00pm

Abstract

 

Note for Attendees

Light refreshments will be served at 2:45pm in ESB 4133, the PIMS Lounge before this colloquium.
hide
UCLA
Fri 14 Sep 2018, 3:00pm
Department Colloquium
ESB 2012
TBA
ESB 2012
Fri 14 Sep 2018, 3:00pm-4:00pm

Abstract

 
hide
 
Top