Date/Time : 24 Jul 2024 15:00
Venue : S17 #04-05 (SR2)
Speaker : Shidong Jiang, Flatiron Institute

In this talk, we will first present an overview of fast integral equation methods (FIEMs). Fast algorithms, such as the fast multipole methods and their descendants, have made profound impacts on many areas of scientific computing. Boundary integral equations of the second kind are the natural formulation for boundary value problems of elliptic partial differential equations due to the reduction of dimensionality by one, automatic satisfaction of conditions at infinity for exterior and scattering problems, and well conditioning. The computational bottleneck that arises because the resulting linear system is dense due to the nonlocal and long-range nature of integral operators is largely removed by fast algorithms. FIEMs have been highly successful in solving a large class of problems in fluid mechanics, elasticity, acoustics, and electromagnetics.

Second, we introduce a new class of multilevel, adaptive, dual-space methods for computing fast convolutional transforms. The DMK (dual-space multilevel kernel-splitting) framework uses a hierarchy of grids, computing a smoothed interaction at the coarsest level, followed by a sequence of corrections at finer and finer scales until the problem is entirely local, at which point direct summation is applied. Unlike earlier multilevel summation schemes, DMK exploits the fact that the interaction at each scale is diagonalized by a short Fourier transform, permitting the use of separation of variables without relying on the FFT. The DMK framework substantially simplifies the algorithmic structure of the fast multipole method (FMM) and unifies the FMM, Ewald summation, and multilevel summation, achieving speeds comparable to the FFT in work per grid point, even in a fully adaptive context.

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Date/Time : 17 Jul 2024 15:00
Venue : via Zoom
Speaker : Feng Shao, Peking University

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https://nus-sg.zoom.us/j/82730991505?pwd=LEzOeoXXrYPflm2EVK5xKzpiQCi6Pt.1

Meeting ID: 827 3099 1505
Passcode: 008679

In this talk, I will discuss the joint work with Dongyi Wei and Zhifei Zhang on the construction of self-similar smooth imploding solutions of isentropic relativistic Euler equations with isothermal equation of state $p=\frac1\ell\varrho$ for all $\ell>1$ in physical space dimension $d=2,3$ and for $\ell>1$ close to 1 in higher dimensions. This work is a crucial step toward solving long-standing open problem: finite time blow-up of the supercritical defocusing nonlinear wave equation.

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Date/Time : 17 Jul 2024 17:00
Venue : LT33 (S17 Level 2)
Speaker : Wojciech Woloszyn, University of Oxford

Two features of the Ultimate L are that it is forcing invariant and compatible with large cardinals. The resurrection principle stabilizes forcing out albeit mildly. The latter can be refuted from the existence of a large cardinal way below I0. What is the bearing of this on the status of large cardinals and the axiom V=Ultimate L? An interesting picture unfolds.

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Date/Time : 16 Jul 2024 15:30
Venue : LT33 (S17 Level 2)
Speaker : Nishant Chandgotia, Tata Institute of Fundamental Research - Centre for Applicable Mathematics

When can a given subset S be tiled by rectangular tiles in Z^2? This is an old question and for answering it Conway and Lagarias introduced certain groups which are now known as the Conway-Lagarias group (1990). Together with some analytic conditions, Thurston noticed that these questions can be answered completely in certain situations. This later formed the basis for understanding what uniformly random tiling of regions looked like (for instance in the results from Cohn, Kenyon and Propp from 2001). In 1995, Klaus Schmidt realised that this was related to a certain cohomology of dynamical systems and initiated its formal study. We will talk about such questions in the context of graph homomorphisms on the Z^d lattice and see how it relates to the word problem of finitely presented groups.

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Date/Time : 12 Jul 2024 14:00
Venue : S17 #04-04 (SR3)
Speaker : Nishant Chandgotia, TIFR CAM (Bangalore)

The dimer model, also referred to as domino tilings or perfect matching, are tilings of the Z^d lattice by boxes exactly one of whose sides has length 2 and the rest have length 1. This is a very well-studied statistical physics model in two dimensions with many tools like height functions and Kasteleyn determinant representation coming to its aid. The higher dimensional picture is a little daunting because most of these tools are limited to two dimensions. In these series of talks I will describe some recent progress in 3 dimensions where we show a large deviations principle for dimer tilings analogous to those by Cohn, Kenyon and Propp (2000). This is joint work with Scott Sheffield and Catherine Wolfram.

The talks should be accessible to a general audience but it will help to have working knowledge of probability and basic ergodic theory.

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Date/Time : 12 Jul 2024 15:00
Venue : S17 #04-05 (SR2)
Speaker : Zhang Zhen, Southern University of Science and Technology

Anisotropic surface diffusion is recently investigated in detail from both modeling and numerical perspectives. While sharp-interface models provide a clear description of the problem, it introduces difficulties in numerical simulations especially when there are topological changes. In this talk, we will present a phase-field approach for modeling anisotropic surface diffusions. We first consider the equilibrium problem of energy minimization. By employing a three-operator splitting technique, we could numerically compute the equilibrium shapes of crystals (ESC) using an optimization approach with mathematical convergence. Then we propose a second-order mass preserving dynamic model as a gradient flow of the anisotropic energy for simulating surface diffusion processes. For surface diffusions in contact with solid substrates, we discuss a regularized thin film model as an approximation of the sharp-interface problem. Numerical results demonstrate the good convergence of these models.

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Date/Time : 10 Jul 2024 14:00
Venue : S17 #04-04 (SR3)
Speaker : Nishant Chandgotia, TIFR CAM (Bangalore)

The dimer model, also referred to as domino tilings or perfect matching, are tilings of the Z^d lattice by boxes exactly one of whose sides has length 2 and the rest have length 1. This is a very well-studied statistical physics model in two dimensions with many tools like height functions and Kasteleyn determinant representation coming to its aid. The higher dimensional picture is a little daunting because most of these tools are limited to two dimensions. In these series of talks I will describe some recent progress in 3 dimensions where we show a large deviations principle for dimer tilings analogous to those by Cohn, Kenyon and Propp (2000). This is joint work with Scott Sheffield and Catherine Wolfram.

The talks should be accessible to a general audience but it will help to have working knowledge of probability and basic ergodic theory.

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Date/Time : 08 Jul 2024 16:00
Venue : S17 #04-06 (SR1)
Speaker : Panel Discussion: Various speakers,

The leap from higher education to industry is a pivotal stage for many graduate students. Emphasising the necessity of an interdisciplinary approach and the application of the robust analytical skills honed during graduate studies, this panel discussion offers a comprehensive exploration of the journey that awaits MSc and PhD graduates who are looking to bridge the gap between academic accomplishment and professional fulfilment in the industry. Panellists will provide candid reflections on their personal pathways, highlighting the obstacles they encountered and the successes they achieved within various industrial domains. Attendees of the session will be encouraged to engage with live inquiries and raise pertinent topics for discussion. Discussions will revolve around the symbiotic relationship between advanced academic preparation and industry expectations, strategic planning for entering the corporate sector, the diverse opportunities ranging from employment in small to large-scale organisations to the launch of deep tech ventures, as well as the innovative trends and fruitful careers found in today’s industrial research and development.

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Date/Time : 04 Jul 2024 14:00
Venue : S16 #03-05/06
Speaker : Libo Li, University of New South Wales, Sydney

We study the upper and lower bounds for prices of European and American style options with the possibility of an external termination, meaning that the contract may be terminated at some random time. Under the assumption that the underlying market model is incomplete and frictionless, we obtain duality results linking the upper price of a vulnerable European option with the price of an American option whose exercise times are constrained to times at which the external termination can happen with a non-zero probability. Similarly, the upper and lower prices for an vulnerable American option are linked to the price of an American option and a game option, respectively. In particular, the minimizer of the game option is only allowed to stop at times which the external termination may occur with a non-zero probability.

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