Idaho

Mon 20 Nov 2017, 4:00pm
Algebraic Geometry Seminar
MATH 126

Equations for surfaces in projective fourspace

MATH 126
Mon 20 Nov 2017, 4:00pm5:00pm
Abstract
This talk is concerned with the question of the minimal number of equations necessary to define a given projective variety schemetheoretically. Every hypersurface is cut out by a single polynomial schemetheoretically (also settheoretically 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 nspace has codimension two, then the minimal number of polynomials necessary to cut out the variety schemetheoretically 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 nonsingular surface in projective fourspace to be cut out by three polynomials.
hide

Institute of Applied Mathematics, UBC

Tue 21 Nov 2017, 12:30pm
Scientific Computation and Applied & Industrial Mathematics
ESB 4133 (PIMS Lounge)

Likelihoodfree methods: Challenges in fitting individualbased models to epidemiological data

ESB 4133 (PIMS Lounge)
Tue 21 Nov 2017, 12:30pm1:30pm
Abstract
Complex individualbased 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 likelihoodfree 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, Markovchain Monte Carlo and maximum likelihood. This is then applied to a complex individualbased simulation for lymphatic filariasis, a human parasitic disease, which affects over 120 million individuals internationally. Finally, I will discuss a new approach to individualbased model fitting by constructing a synthetic likelihood using mixture density networks.
hide

University of Chile

Tue 21 Nov 2017, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
ESB 2012

Asymptotic stability for some nonlinear KleinGordon equations for odd perturbations in the energy space

ESB 2012
Tue 21 Nov 2017, 3:30pm4:30pm
Abstract
Showing asymptotic stability in one dimensional nonlinear KleinGordon 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, 4:00pm5:00pm
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, 2:00pm3:00pm
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, 3:00pm4:00pm
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 selfavoiding 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 6,3sphere and a conjecture of Suslin.

ESB 4133 (PIMS Lounge)
Wed 22 Nov 2017, 3:15pm4:15pm
Abstract
The algebraic Ktheory, due to Quillen, of a field is related to a theory defined by Milnor called Milnor Ktheory 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 (n1)! 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, 4:00pm5:00pm
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, 4:00pm5:00pm
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 nontrivial padic representation of the fundamental group of X, which arises from geometry, is nontrivial mod p^N.
hide


Wed 29 Nov 2017, 2:45pm
SPECIAL
ESB 4133 (PIMS Lounge)

Nov. 29th PIMS Afternoon Tea has been moved to 4:30pm5:00pm

ESB 4133 (PIMS Lounge)
Wed 29 Nov 2017, 2:45pm3:15pm
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, 4:00pm5:00pm
Abstract
TBA
hide

Université ParisSaclay

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, 5:00pm6:00pm
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.
hide

Université ParisSaclay

Thu 30 Nov 2017, 5:00pm
SPECIAL
ESB 2012

UBC Mathematics Lecture Series:: Regularized Optimal Transport. Part I.

ESB 2012
Thu 30 Nov 2017, 5:00pm6:30pm
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 nondifferentiability 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.
hide

Courant Institute, NYU

Fri 1 Dec 2017, 3:00pm
SPECIAL
Department Colloquium
ESB 2012

PIMSUBC Distinguished ColloquiumMicroscopic description of Coulombtype systems

ESB 2012
Fri 1 Dec 2017, 3:00pm4:00pm
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 GinzburgLandau 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.
hide

Université ParisSaclay

Fri 1 Dec 2017, 5:00pm
SPECIAL
ESB 2012

UBC Mathematics Lecture Series: Regularized Optimal Transport. Part II

ESB 2012
Fri 1 Dec 2017, 5:00pm6:30pm
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 nondifferentiability 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.
hide

University of Lethbridge

Thu 4 Jan 2018, 3:30pm
Number Theory Seminar
TBA

TBA

TBA
Thu 4 Jan 2018, 3:30pm10:00am
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, 3:30pm5:00pm
Abstract
hide

UCDavies

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, 3:30pm4:30pm
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, 4:00pm5:00pm
Details
hide

SNS, Pisa

Fri 2 Mar 2018, 3:00pm
SPECIAL
Department Colloquium
ESB2012

PIMSUBC Distinguished ColloquiumTBA

ESB2012
Fri 2 Mar 2018, 3:00pm4:00pm
Abstract
hide

UBC Math

Fri 9 Mar 2018, 3:00pm
Department Colloquium
ESB 2012

Graduate Research Award: TBA

ESB 2012
Fri 9 Mar 2018, 3:00pm4:00pm
Abstract
hide

UBC Math

Fri 16 Mar 2018, 3:00pm
Department Colloquium
ESB 2012

Graduate Research Award: TBA

ESB 2012
Fri 16 Mar 2018, 3:00pm4:00pm
Abstract
hide

Oregon

Mon 19 Mar 2018, 4:00pm
Algebraic Geometry Seminar
MATH 126

TBA

MATH 126
Mon 19 Mar 2018, 4:00pm5:00pm
Abstract
TBA
hide

UBC Math

Fri 23 Mar 2018, 3:00pm
Department Colloquium
ESB 2012

Graduate Research Award: TBA

ESB 2012
Fri 23 Mar 2018, 3:00pm4:00pm
Abstract
hide

MIT

Tue 27 Mar 2018, 4:00pm
Discrete Math Seminar
ESB 4127

TBD

ESB 4127
Tue 27 Mar 2018, 4:00pm5:00pm
Abstract
hide

University of Bordeaux

Thu 29 Mar 2018, 3:30pm
Number Theory Seminar

TBA

Thu 29 Mar 2018, 3:30pm5:00pm
Abstract
hide

University of Oxford

Fri 6 Apr 2018, 3:00pm
Department Colloquium
ESB 2012

PIMSUBC Distinguished ColloquiumTBA

ESB 2012
Fri 6 Apr 2018, 3:00pm4:00pm
Abstract
hide

UCLA

Fri 14 Sep 2018, 3:00pm
Department Colloquium
ESB 2012

TBA

ESB 2012
Fri 14 Sep 2018, 3:00pm4:00pm
Abstract
hide

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.