
11:00 am
Yian Ma  UCSD
MCMC vs. variational inference  for credible learning and decision making at scale
Center for Computational Mathematics Seminar
Zoom ID 922 9012 0877
AbstractI will introduce some recent progress towards understanding the scalability of Markov chain Monte Carlo (MCMC) methods and their comparative advantage with respect to variational inference. I will discuss an optimization perspective on the infinite dimensional probability space, where MCMC leverages stochastic sample paths while variational inference projects the probabilities onto a finite dimensional parameter space. Three ingredients will be the focus of this discussion: nonconvexity, acceleration, and stochasticity. This line of work is motivated by epidemic prediction, where we need uncertainty quantification for credible predictions and informed decision making with complex models and evolving data.

1:00 pm
Elizabeth Tatum  UIUC
Towards Splitting $BP \langle 2 \rangle \wedge BP\langle 2 \rangle$ at Odd Primes
Math 292  Topology seminar
https://ucsd.zoom.us/j/99777474063
Password: topology
AbstractIn the 1980s, Mahowald and Kane used BrownGitler spectra to construct splittings of $bo \wedge bo$ and $l \wedge l$.These splittings helped make it feasible to do computations using the $bo$ and $l$based Adams spectral sequences.I will discuss progress towards an analogous splitting for $BP\langle 2 \rangle \wedge BP \langle 2 \rangle$ at odd primes.

2:30 pm
Scotty Tilton  UCSD
Morava's orbit picture and Morava stabilizer groups
Math 292  Topology seminar (student talk series on chromatic homotopy theory)
https://ucsd.zoom.us/j/99777474063
Password: topology

4:00 pm
Jonathan Zhu  Princeton University
Minmax Theory for Capillary Surfaces
Department Colloquium
Zoom ID: 964 0147 5112
Password: ColloquiumAbstractCapillary surfaces model interfaces between incompressible immiscible fluids. The EulerLagrange equations for the capillary energy functional reveals that such surfaces are solutions of the prescribed mean curvature equation, with prescribed contact angle where the interface meets the container of the fluids. Minmax methods have been used with great success to construct unstable critical points of various energy functionals, particularly for the special case of closed minimal surfaces. We will discuss the development of minmax methods to construct general capillary surfaces.

11:00 am
Gunhee Cho  UCSB
The lower bound of the integrated Carath ÌeodoryReiffen metric and Invariant metrics on complete noncompact Kaehler manifolds
Math 258  Seminar in Differential Geometry
AP&M Room 7321
Zoom ID: 949 1413 1783AbstractWe seek to gain progress on the following longstanding conjectures in hyperbolic complex geometry: prove that a simply connected complete K Ìˆahler manifold with negatively pinched sectional curvature is biholomorphic to a bounded domain and the Carath ÌeodoryReiffen metric does not vanish everywhere. As the next development of the important recent results of D. Wu and S.T. Yau in obtaining uniformly equivalence of the base K Ìˆahler metric with the Bergman metric, the KobayashiRoyden metric, and the complete Ka ÌˆhlerEinstein metric in the conjecture class but missing of the Carath ÌeodoryReiffen metric, we provide an integrated gradient estimate of the bounded holomorphic function which becomes a quantitative lower bound of the integrated Carath ÌeodoryReiffen metric. Also, without requiring the negatively pinched holomorphic sectional curvature condition of the Bergman metric, we establish the equivalence of the Bergman metric, the KobayashiRoyden metric, and the complete Ka ÌˆhlerEinstein metric of negative scalar curvature under a bounded curvature condition of the Bergman metric on an ndimensional complete noncompact Ka Ìˆhler manifold with some reasonable conditions which also imply nonvanishing Carath ÌedoroyReiffen metric. This is a joint work with KyuHwan Lee.

11:00 am
Joshua Frisch  ENS Paris
The Infinite Conjugacy Class Property and its Applications in Random Walks and Dynamics
Department Colloquium
Zoom ID: 964 0147 5112
Password: ColloquiumAbstractA group is said to have the infinite conjugacy class (ICC) property if every nonidentity element has an infinite conjugacy class. In this talk I will survey some ideas in geometric group theory, harmonic functions on groups, and topological dynamics and show how the ICC property sheds light on these three seemingly distinct areas. In particular I will discuss when a group has only constant bounded harmonic functions, when every proximal dynamical system has a fixed point, and what this all has to do with the growth of a group. No prior knowledge of harmonic functions on groups or Topological dynamics will be assumed.
This talk will include joint work with Anna Erschler, Yair Hartman, Omer Tamuz, and Pooya Vahidi Ferdowsi.

11:00 am
Gaultier Lambert  University of Zurich
Normal approximation for traces of random unitary matrices
Math 288  Probability and Statistics
For zoom ID and password email: ynemish@ucsd.edu

12:00 pm
Sebastián Barbieri  Universidad de Santiago de Chile
Selfsimulable groups
Math 211B  Group Actions Seminar
Zoom ID 967 4109 3409
Email an organizer for the passwordAbstractWe say that a finitely generated group is selfsimulable if every action of the group on a zerodimensional space which is effectively closed (this means it can be described by a Turing machine in a specific way) is the topological factor of a subshift of finite type on said group. Even though this seems like a property which is very hard to satisfy, we will show that these groups do exist and that their class is stable under commensurability and quasiisometries of finitely presented groups. We shall present several examples of wellknown groups which are selfsimulable, such as Thompson's V and higherdimensional general linear groups. We shall also show that Thompson's group F satisfies the property if and only if it is nonamenable, therefore giving a computability characterization of this wellknown open problem. Joint work with Mathieu Sablik and Ville Salo.

2:00 pm
German Enciso  UC Irvine
Absolutely Robust Control Modules in Chemical Reaction Networks
Math 218  Seminars on Mathematics for Complex Biological Systems
Contact Bo Li at bli@math.ucsd.edu for the Zoom info
AbstractWe use ideas from the theory of absolute concentration robustness to control a species of interest in a given chemical reaction network. The results are based on the network topology and the deficiency of the system, independent of reaction parameter values. The control holds in the stochastic regime and the quasistationary distribution of the controlled species is shown to be approximately Poisson under a specific scaling limit.
https://mathweb.ucsd.edu/~bli/research/mathbiosci/MBBseminar/

2:00 pm
Petar Bakic  Utah
Howe Duality for Exceptional Theta Correspondences
Math 209  Number Theory Seminar
Pretalk at 1:20 PM
APM 6402 and Zoom;
See https://www.math.ucsd.edu/~nts/ AbstractThe theory of local theta correspondence is built up from two main ingredients: a reductive dual pair inside a symplectic group, and a Weil representation of its metaplectic cover. Exceptional correspondences arise similarly: dual pairs inside exceptional groups can be constructed using socalled Freudenthal Jordan algebras, while the minimal representation provides a suitable replacement for the Weil representation. The talk will begin by recalling these constructions. Focusing on a particular dual pair, we will explain how one obtains Howe duality for the correspondence in question. Finally, we will discuss applications of these results. The new work in this talk is joint with Gordan Savin.

10:30 am
Sergej Monavari  Utrecht University
Double nested Hilbert schemes and stable pair invariants
Math 208  Algebraic Geometry Seminar
Pretalk at 10:00 AM
Contact Samir Canning (srcannin@ucsd.edu) for zoom access.
AbstractHilbert schemes of points on a smooth projective curve are simply symmetric powers of the curve itself; they are smooth and we know essentially everything about them. We propose a variation by studying double nested Hilbert schemes of points, which parametrize flags of 0dimensional subschemes satisfying certain nesting conditions dictated by Young diagrams. These moduli spaces are almost never smooth but admit a virtual structure à la BehrendFantechi. We explain how this virtual structure plays a key role in (re)proving the correspondence between GromovWitten invariants and stable pair invariants for local curves, and say something on their Ktheoretic refinement.

10:00 am
Jurij Volcic  Copenhagen University
Ranks of linear pencils separate similarity orbits of matrix tuples
Math 243  Functional Analysis Seminar
Please email djekel@ucsd.edu for Zoom details
AbstractThe talk addresses the conjecture of Hadwin and Larson on joint similarity of matrix tuples, which arose in multivariate operator theory.
The main result states that the ranks of linear matrix pencils constitute a collection of separating invariants for joint similarity of matrix tuples, which affirmatively answers the twosided version of the said conjecture. That is, mtuples X and Y of n×n matrices are simultaneously similar if and only if rk L(X) = rk L(Y) for all linear matrix pencils L of size mn. Similar results hold for certain other group actions on matrix tuples. On the other hand, a pair of matrix tuples X and Y is given such that rk L(X) <= rk L(Y) for all L, but X does not lie in the closure of the joint similarity orbit of Y; this constitutes a counterexample to the general HadwinLarson conjecture.
The talk is based on joint work with Harm Derksen, Igor Klep and Visu Makam.