Mathematics
http://events.berkeley.edu/index.php/calendar/sn/math.html
Upcoming EventsThematic Seminar, Jan 15
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122704&date=2019-01-15
Density functional theory is an effective tool in solid state physics and quantum chemistry for electronic structure calculation. However, it has difficulties when dealing with strongly correlated systems. In this talk, we examine the regime where the electrons are strictly correlated. This gives rise to a multimarginal optimal transport problem, a direct extension of the optimal transport problem that has applications in economics and operations research as well. In particular we introduce methods from convex optimization to provide a lower bound to the cost of the multimarginal transport problem with a practical running time. We further propose projection schemes based on tensor decomposition to obtain upper bounds to the energy. Numerical experiments demonstrate a gap of order $10^{-3}$ to $10^{-2}$ between the upper and lower bounds.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122704&date=2019-01-15Seminar 217, Risk Management: Instrumental variables as bias amplifiers with general outcome and confounding, Jan 22
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122084&date=2019-01-22
Drawing causal inference with observational studies is the central pillar of many disciplines. One sufficient condition for identifying the causal effect is that the treatment-outcome relationship is unconfounded conditional on the observed covariates. It is often believed that the more covariates we condition on, the more plausible this unconfoundedness assumption is. This belief has had a huge impact on practical causal inference, suggesting that we should adjust for all pretreatment covariates. However, when there is unmeasured confounding between the treatment and outcome, estimators adjusting for some pretreatment covariate might have greater bias than estimators that do not adjust for this covariate. This kind of covariate is called a bias amplifier and includes instrumental variables that are independent of the confounder and affect the outcome only through the treatment. Previously, theoretical results for this phenomenon have been established only for linear models. We fill this gap in the literature by providing a general theory, showing that this phenomenon happens under a wide class of models satisfying certain monotonicity assumptions.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122084&date=2019-01-22Differential Geometry Seminar, Jan 22
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122775&date=2019-01-22
We show that each fixed point component of an isometric torus action of a 5 torus has the rational cohomology of a rank one symmetric space. We give various applications.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122775&date=2019-01-22Thematic Seminar, Jan 22
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122731&date=2019-01-22
Vasy will discuss, based on joint work with Peter Hintz, the stability of the family of Kerr-de Sitter (KdS) black holes, which are rotating black holes in a spacetime with positive cosmological constant, as solutions of Einstein's vacuum equation: spacetimes evolving from initial data close to those of a KdS metric stay globally close to this KdS spacetime, and are indeed asymptotic to a nearby member of the KdS family.<br />
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Vasy will discuss the general setup and formulate the result, and then in the second half of the talk focus on general analytic aspects of this problem, involving global analysis, together with the choice of a gauge to break the diffeomorphism invariance of Einstein's equation and the role of constraint damping which has also played a key role in numerical general relativity (and thus LIGO and the detection of gravitational waves).http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122731&date=2019-01-22Thematic Seminar, Jan 23
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122835&date=2019-01-23
Families of algebraic manifolds give interesting examples of discrete subgroups of Lie groups, via their monodromy. They also lead to differential equations, such as the hypergeometric ones, whose solutions have an arithmetic significance. After providing the necessary background I will explain a connection to dynamical invariants called Lyapunov exponents, which reveals special geometric features ofthe discrete groups and the corresponding differential equations.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122835&date=2019-01-23Paris/Berkeley/Bonn/Zürich Analysis Seminar, Jan 24
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122605&date=2019-01-24
In this talk, we study the long time behaviour of some stochastic partial differential equations (SPDEs). After introducing the notions of ergodicity, unique ergodicity and convergence to equilibrium, we will discuss how these have been proven for a very large class of parabolic SPDEs.<br />
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We will then shift our attention to dispersive SPDEs, where the general strategy for the parabolic case fails. We will describe this failure for wave equation on the 1-dimensional torus and present a result that settles unique ergodicity even in this case.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122605&date=2019-01-24Thematic Seminar, Jan 24
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122836&date=2019-01-24
Let $M_g$ be the moduli space of smooth curves of genus $g$. The tautological ring is a subring of the cohomology of $M_g$ that was introduced by Mumford in the 1980s in analogy with the cohomology of Grassmannians. Work of Faber and Faber-Zagier in the 1990s led to two competing conjectural descriptions of the structure of the tautological ring. After reviewing these conjectures, I will discuss some of the evidence in recent years favoring one conjecture over the other.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122836&date=2019-01-24Thematic Seminar, Jan 25
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122837&date=2019-01-25
The classical $q$-hypergeometric orthogonal polynomials are assembled into a hierarchy called the $q$-Askey scheme. It is now a classical subject to study the combinatorics of their coefficients and their moments. The polynomials admit a generalization leading to remarkable orthogonal polynomials in several variables. The most general family is the Macdonald-Koornwinder polynomials and Macdonald polynomials associated to any classical root system can be expressed as limits or special cases of Macdonald-Koornwinder polynomials. Understanding the combinatorics of these polynomials is an important open problem. In this talk we will show some recent progress related to special cases of these polynomials.<br />
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We will highlight combinatorial formulas for<br />
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1. Certain Macdonald-Koornwinder polynomials using exclusion processes with open boundaries and tableaux combinatorics (arXiv:1510.05023)<br />
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2. Macdonald polynomials of type A using exclusion processes and multiline queues (arXiv:1811.01024)<br />
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3. Multivariate $q$-Little Jacobi polynomials thanks to Lecture Hall Tableaux (arXiv:1804.02489)<br />
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This talk will be about enumerative, algebraic and asymptotics combinatorics. No prior knowledge is required. Open problems will be presented.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122837&date=2019-01-25Probabilistic Operator Algebra Seminar, Jan 28
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122179&date=2019-01-28
We present an alternative approach to the theory of free Gibbs states with convex potentials. Instead of solving SDE's, we combine PDE techniques with a notion of asymptotic approximability by trace polynomials for a sequence of functions on $M_N(\mathbb C)_{sa}^m$ to prove the following. Suppose $\mu _N$ is a probability measure on $M_N(\mathbb C)_{sa}^m$ given by uniformly convex and semi-concave potentials $V_N$, and suppose that the sequence $DV_N$ is asymptotically approximable by trace polynomials. Then the moments of $\mu _N$ converge to a noncommutative law λ. Moreover, the free entropies $\chi (\lambda )$, $\underline {\chi }(\lambda )$, and $\chi ^*(\lambda )$ agree and equal the limit of the normalized classical entropies of $\mu _N$. We also sketch further applications to conditional expectations, relative entropy, and free transport for these free Gibbs states.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122179&date=2019-01-28Seminar 217, Risk Management: The coordination of centralised and distributed generation, Jan 29
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122085&date=2019-01-29
We analyse the interaction between centralised carbon-emissive technologies and distributed non-emissive technologies. A representative consumer can satisfy her electricity demand by investing in solar panels and by buying power from a centralised firm. We consider the point of view of the consumer, the firm and a social planner, formulating suitable McKean-Vlasov control problems with stochastic coefficients. First, we provide explicit formulas for the production strategies which minimise the costs. Then, we look for an equilibrium price. Joint work with René Aid and Huyen Pham.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122085&date=2019-01-29Student Harmonic Analysis and PDE Seminar (HADES), Jan 29
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122840&date=2019-01-29
The Remez inequality for polynomials states that the maximum of the polynomial over an interval is controlled by its maximum over a subset of the interval of positive measure. The coefficient in the inequality depends on the degree of the polynomial and the result holds in higher dimensions.<br />
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We give a version of the Remez inequality for solutions of second order linear elliptic PDEs and their gradients. In this context, the degree of a polynomial is replaced by the Almgren frequency of the solution. We discuss other results on quantitative unique continuation for solutions of elliptic PDEs and their gradients and give some applications for the estimates of eigenfunctions for the Laplace-Beltrami operator. The talk is based on a joint work with A. Logunov.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122840&date=2019-01-29Topology Seminar (Introductory Talk), Jan 30
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122838&date=2019-01-30
Fix a suitable (non-elementary) map $f$ from a closed surface $S$ into a closed hyperbolic 3-manifold $M$, and consider the moduli space of harmonic maps homotopic to $f$ and with respect to varying metrics on $S$ and $M$ (the metrics on $M$ are assumed to be negatively curved). We show that the set of such metrics for which the corresponding harmonic map is in Whitney's general position is an open, dense, and connected subset of this moduli space. One application of this result is the proof of the special case of the Simple Loop conjecture when $M$ is hyperbolic.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122838&date=2019-01-30Topology Seminar (Main Talk), Jan 30
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122839&date=2019-01-30
Fix a suitable (non-elementary) map $f$ from a closed surface $S$ into a closed hyperbolic 3-manifold $M$, and consider the moduli space of harmonic maps homotopic to $f$ and with respect to varying metrics on $S$ and $M$ (the metrics on $M$ are assumed to be negatively curved). We show that the set of such metrics for which the corresponding harmonic map is in Whitney's general position is an open, dense, and connected subset of this moduli space. One application of this result is the proof of the special case of the Simple Loop conjecture when $M$ is hyperbolic.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122839&date=2019-01-30Seminar 217, Risk Management:, Feb 5
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122086&date=2019-02-05
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122086&date=2019-02-05Center for Computational Biology Seminar, Feb 6
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=120946&date=2019-02-06
Genomics, genetic rescue, and the future of conservation<br />
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Abstract: New technologies, including complete genome sequencing and genome engineering, promise to revolutionize conservation and slow the pace of the ongoing extinction crisis. However, the value of these technologies to conservation remains unclear. Using mountain lions from across their range and wolves from Isle Royale as examples, I will explore the value of complete genome reconstruction and analysis to conservation and management, focusing on what complete genomes can reveal that traditional genetic approaches cannot. I will also discuss the potential of genomics to inform genetic rescue interventions, and highlight some of the technical, ethical, and environmental hurdles that these particularly controversial technologies still face.<br />
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Bio: Beth Shapiro is an evolutionary biologist who specializes in the genetics of ice age animals and plants. As Professor of Ecology and Evolutionary Biology at UC Santa Cruz and HHMI Investigator, Beth uses DNA recovered from bones and other remains to study how species evolved through time and how human activities have affected and continue to affect this dynamic process. Her work focuses on organisms ranging from influenza to mammoths, asking questions about domestication, admixture, speciation, and pathogen evolution. Her current work develops techniques to recover increasingly trace amounts of DNA such as from environmental and forensic samples.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=120946&date=2019-02-06Applied Math Seminar, Feb 7
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122772&date=2019-02-07
In this talk we discuss how to compute derivatives of long-time-averaged objectives with respect to multiple system parameters in chaotic systems, via the recently developed non-intrusive least-squares adjoint shadowing (NILSAS) algorithm.<br />
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First we review how to compute such derivatives via comparing the base trajectory and a shadowing trajectory, which is a new trajectory with perturbed parameter and perturbed initial condition, yet always lies close to the base trajectory. Then we review how to compute such shadowing trajectory via a `non-intrusive' minimization problem on the unstable subspace. Then we show our recent work on defining and proving the unique existence of adjoint shadowing directions. Then we develop the NILSAS algorithm, whose cost is independent of number of parameters, and its implementation requires only minor modifications to existing adjoint solvers. Finally, we show an application, by Chaitanya Talnikar, of NILSAS on a weakly turbulent flow over a three-dimensional cylinder at Re=1100, where the cost of NILSAS is similar to simulating the flow problem.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122772&date=2019-02-07Probabilistic Operator Algebra Seminar, Feb 11
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122178&date=2019-02-11
It is known that the property of being free (or asymptotically free) for Haar unitaries remains to some extent, when the unitaries are tensored with other unitaries. In the recent years, we investigated the question of, to which extent this property holds. For example, does it hold when tensored by non-unitary operators ? When does asymptotic freeness hold strongly (in norm) ? In traffics ? etc. We have complete answers to some questions, and partial answers to others. I will review what is known at this point. This talk is based on various papers in collaboration with people including Charles Bordenave (CNRS), Camille Male (CNRS), and Pierre Ives Gaudreau Lamarre (Princeton).http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122178&date=2019-02-11Chiwei Yan - Transportation Optimization: Data-enabled Advances in a Sharing Economy, Feb 11
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122323&date=2019-02-11
Abstract: The transportation and logistics industries are undergoing a round of revolutionary innovation. This innovation is fueled by two key drivers: (1) the growing availability of data, and (2) new operational paradigms in a sharing economy. This talk focuses on showcasing how new models, enabled by the prevalence of data, can lead to significant value in operational decision-making.<br />
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We begin by presenting our research that shows how trip data in bike-sharing systems can be mined to infer rider substitution behaviors when there are bike or dock shortages. Based on a non-parametric ranking-based choice model, we propose efficient enumeration procedures and first-order methods to solve the large-scale estimation problem by exploiting problem structure. We prove consistency results of our method. We then demonstrate, with Boston Hubway data, that ridership can be significantly improved through effective inventory allocation operations with better demand modeling.<br />
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Next, we describe a recent work in which we propose a new car-pooling mechanism in ride-hailing, called dynamic waiting which varies rider waiting before dispatch. The goal is to limit price volatility in ride-hailing services by reducing the role of surge pricing. We describe a steady-state model depicting the long-run average performance of a ride-hailing service, and characterize the system equilibrium. Calibrating the model using Uber data, we reveal insights on welfare-maximizing pricing and waiting strategies. We show that, with dynamic waiting, price can be lowered, its variability is mitigated and total welfare is increased. <br />
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Bio: Chiwei Yan received his PhD from the Operations Research Center at MIT in 2017. His current research interest is in transportation and logistics, with a focus on data-driven optimization and emerging problems in a sharing economy. He is a recipient of the Best Dissertation Award Honorable Mention and the Outstanding Paper Award in Air Transportation from INFORMS Transportation Science and Logistics Society, the Best Dissertation Award from INFORMS Aviation Application Section, the AGIFORS Anna Valicek Award, and the UPS Doctoral Fellowship, among others. His research involves collaborations with both the private and public sectors, including the Federal Aviation Administration, Sabre Airline Solutions, Boston Hubway Bikes and Uber. Before coming to MIT, he obtained the Bachelor of Science in Industrial Engineering from Tsinghua University.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122323&date=2019-02-11Seminar 217, Risk Management:, Feb 12
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122087&date=2019-02-12
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122087&date=2019-02-12Beste Basciftci - Value of Optimization under Uncertainty and Integration of Data in Energy Supply Chains, Feb 15
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122433&date=2019-02-15
Abstract: Most of the real-life problems involve uncertainty, which need to be delicately integrated into the decision-making processes. In this talk, we present various stochastic optimization techniques motivated by maintenance, operations and capacity expansion planning problems in energy systems. In the first part of the talk, our aim is to effectively model and solve the integrated condition-based maintenance and operations scheduling problem of a fleet of generators. We develop a data-driven optimization framework that explicitly considers the effect of the sensor-driven generator failure scenarios and operations schedules on the generators’ degradation levels to construct a reliable and cost-efficient plan. In the second part of the talk, we shift our focus to a more generic problem setting in sequential decision-making under uncertainty. Although two-stage and multi-stage stochastic programming are among the key methodologies to address multi-period problems under uncertainty, they might not provide adequate solutions under limited flexibility by resulting in either fully static or dynamic policies. We propose a novel adaptive stochastic programming approach, in which we optimize the time to revise decisions. We provide theoretical bounds on the performance of the proposed approach compared to the static and dynamic approaches, and present practical implications of the choice of the revision time. We also tailor solution algorithms using our analytical analyses and derive their approximation guarantees. To illustrate our results, we study a generation expansion planning problem demonstrating the advantages of the adaptive approach over existing policies. <br />
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Bio: Beste Basciftci is currently a PhD candidate in Operations Research at the H. Milton Stewart School of Industrial and Systems Engineering, Georgia Institute of Technology, with a minor in Statistics. She received her bachelor's degrees in Industrial Engineering and Computer Engineering from Boğaziçi University with High Honors. She also hold a master's degree in Industrial Engineering from Boğaziçi University. She is broadly interested in data-driven decision making problems under uncertainty. Methodologically, her research focuses on developing mixed-integer, stochastic programming and distributionally robust optimization approaches to address operations research/management related problems, specifically for applications in energy, supply chains, production systems, and healthcare operations. Her research also involves developing and integrating statistical modeling and business analytics approaches to the subsequent decision-making processes.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122433&date=2019-02-15Seminar 217, Risk Management:, Feb 19
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122088&date=2019-02-19
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122088&date=2019-02-19Seminar 217, Risk Management:, Feb 26
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122089&date=2019-02-26
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122089&date=2019-02-26Seminar 217, Risk Management:, Mar 5
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122090&date=2019-03-05
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122090&date=2019-03-05Center for Computational Biology Seminar, Mar 6
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=120948&date=2019-03-06
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=120948&date=2019-03-06Seminar 217, Risk Management:, Mar 12
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122091&date=2019-03-12
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122091&date=2019-03-12Seminar 217, Risk Management:, Mar 19
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122092&date=2019-03-19
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122092&date=2019-03-19Topology Seminar (Introductory Talk), Mar 20
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122773&date=2019-03-20
I'll introduce three ways to build hyperbolic manifolds: arithmetic groups, "interbreeding", and "inbreeding". The first is purely algebraic. The second leads to the famous nonarithmetic examples of Gromov and Piatetski-Shapiro. The third is due to Agol, further studied by Belolipetsky-Thomson. Further, we will discuss concrete 3-dimensional examples via links in $S^3$ and belted sums.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122773&date=2019-03-20Topology Seminar (Main Talk), Mar 20
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122774&date=2019-03-20
I will explain why large classes of non-arithmetic hyperbolic $n$-manifolds, including the hybrids introduced by Gromov and Piatetski-Shapiro and many of their generalizations, have only finitely many finite-volume immersed totally geodesic hypersurfaces, answering a question of Reid and (independently) McMullen for $n=3$. These are the first examples of finite-volume $n$-hyperbolic manifolds, $n >2$, for which the collection of all finite-volume totally geodesic hypersurfaces is finite but nonempty. In this talk, I will focus mostly on dimension 3, where one can even construct link complements with this property. This is joint work with David Fisher, Jean-François Lafont, and Nicholas Miller.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122774&date=2019-03-20Seminar 217, Risk Management:, Apr 2
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122093&date=2019-04-02
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122093&date=2019-04-02Center for Computational Biology Seminar, Apr 3
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=120951&date=2019-04-03
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=120951&date=2019-04-03Seminar 217, Risk Management:, Apr 9
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122094&date=2019-04-09
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122094&date=2019-04-09Seminar 217, Risk Management:, Apr 16
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122096&date=2019-04-16
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122096&date=2019-04-16Probabilistic Operator Algebra Seminar, Apr 22
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122407&date=2019-04-22
The Aronszajn-Donoghue theorem provides a good understanding of the subtle theory of rank one perturbations. One of their statements consists of the mutual singularity of the singular parts of the spectral measures under rank one perturbations. For higher rank perturbations, simple examples show that the singular parts can behave more complicatedly. Nonetheless, a 'vector' version of the mutual singularity of the singular parts and a modified Aleksandrov spectral averaging prevail in the finite rank setting. Applications of these results yield further restrictions of the singular spectrum under finite rank perturbations. The presentation is based on joint work with Sergei Treil.http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122407&date=2019-04-22Seminar 217, Risk Management:, Apr 23
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122095&date=2019-04-23
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122095&date=2019-04-23Seminar 217, Risk Management:, Apr 30
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122097&date=2019-04-30
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=122097&date=2019-04-30Center for Computational Biology Seminar, May 1
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=120953&date=2019-05-01
http://events.berkeley.edu/index.php/calendar/sn/math.html?event_ID=120953&date=2019-05-01