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 Events
UBC
Mon 22 Oct 2018, 4:05pm
Algebraic Geometry Seminar
MATH 126
Bivariant Theories and Algebraic Cobordism of Singular Varieties
MATH 126
Mon 22 Oct 2018, 4:05pm-5:05pm

Abstract

I will outline the construction of a natural bivariant theory extending algebraic bordism, which will yield an extension of algebraic cobordism to singular varieties. I will also discuss the connections of this theory to algebraic K-theory and to intersection theory.
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Department of Mathematics, University of Waterloo
Tue 23 Oct 2018, 12:00pm
Scientific Computation and Applied & Industrial Mathematics
ESB 4133 (PIMS Lounge) Please note it starts 30 mins. earlier than the usual time.
Solving DNN Relaxations of the Quadratic Assignment Problem with ADMM and Facial Reduction
ESB 4133 (PIMS Lounge) Please note it starts 30 mins. earlier than the usual time.
Tue 23 Oct 2018, 12:00pm-1:00pm

Abstract

The quadratic assignment problem, QAP, has many applications ranging from the planning of building locations of a university, to the positioning of modules on a computer chip (VLSI design), to the design of keyboards. This problem is arguably one of the hardest of the NP-hard problems, as problems with dimension 30 are still considered hard to solve to optimality.

The QAP in the trace formulation is modelled as the minimization of a quadratic function over the permutation matrices. The set of permutation matrices can be represented by quadratic constraints. Relaxations of these constraints are used in branch and bound solution methods. These relaxations include the eigenvalue and projected eigenvalue relaxations, as well as various semidefinite programming, SDP,  and doubly nonnegative, DNN, relaxations. These latter relaxations are particularly strong and often solve the QAP to optimality. However, they can be extremely expensive to solve.

 We show that the combination of an alternating directions method of multipliers, ADMM, in combination with facial reduction works extremely well in solving the very difficult DNN relaxation.

Note for Attendees

Sushi will be served.
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Hyunju Kwon
UBC
Tue 23 Oct 2018, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
MATH 105
Global Navier-Stokes flows for non-decaying initial data with slowly decaying oscillation
MATH 105
Tue 23 Oct 2018, 3:30pm-4:30pm

Abstract

We consider the Cauchy problem of 3D incompressible Navier-Stokes equations for uniformly locally square integrable initial data. The existence of a time-global weak solution has been known, when the square integral of the initial datum on a ball vanishes as the ball goes to infinity. For non-decaying data, however, the only known global solutions are either for perturbations of constants or when the velocity gradients are in Lp with finite p. In this talk, I will outline how to construct global weak solutions for general non-decaying initial data whose local oscillations slowly decay.
This is a joint work with Tai-Peng Tsai.
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Ethan White
UBC
Tue 23 Oct 2018, 4:00pm
Discrete Math Seminar
ESB 4127
The Triangle-Free Process
ESB 4127
Tue 23 Oct 2018, 4:00pm-5:00pm

Abstract

This is the first part of a two part exposition on the triangle-process. The triangle-free process begins on an empty graph and adds edges at random, provided no triangle is created with the existing edges. One of the original motivations for the process came from Ramsey Theory. Spencer conjectured that the maximum size of an independent set in a graph resulting from the process should be relatively small, and so the triangle-free process would provide constructions for lower bounds on the Ramsey number R(3,t). Recently, Bohman and Keevash obtained new estimates on independence number of such graphs, which gives a lower bound on R(3,t) within a factor of 4+o(1) of the best know upper bound. 

In this first part we will introduce random graph processes with an emphasis on the triangle-free process and the odd-cycle-free process.



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Mathematics, SFU
Wed 24 Oct 2018, 3:00pm
Mathematical Biology Seminar
ESB 4127
Connecting genomic data with vaccine design through modelling
ESB 4127
Wed 24 Oct 2018, 3:00pm-3:45pm

Abstract


While vaccines are available and are effective in protecting against colonisation and disease with Streptococcus pneumoniae, their effectiveness is limited by strain (serotype) replacement following widespread vaccination. Understanding the post-vaccination balance of serotypes would present the opportunity to achieve a final population composed of the most benign (non-invasive) strains. However, the complex ecology of the pneumococcus makes it difficult to predict the post-vaccination balance of strains. Recently, Corander et al proposed that there is widespread apparent negative frequency-dependent selection (NFDS) in the pneumococcus (Corander et al 2017 Nat. Ecol. Evol.).

Here, we use this principle to develop a deterministic model of pneumococcal strain dynamics, and use the model to make predictions about the ecological response of the pneumococcal population to new candidate vaccine strategies. We find that we can identify formulations that out-perform existing formulations in the model. Furthermore, it is possible to obtain a final model population that scores as well as the currently used formulation, using a vaccine strategy with fewer serotypes -- these formulations would be much less costly to produce than current vaccines. We suggest that this approach could provide a template for principled vaccine design based on global surveillance data and genomics.

This is joint work with N. Croucher.
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Ander Holroyd
Wed 24 Oct 2018, 4:00pm
Probability Seminar
ESB 2012
TBA
ESB 2012
Wed 24 Oct 2018, 4:00pm-5:00pm

Abstract


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