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Calendar: Events for week of May 21, 2018

May 21

1:00 pm

1:00 pm

Cedric De Groote

“On Kragh’s ‘Homotopy Equivalence of Nearby Lagrangians and the Serre Spectral Sequence’”

“On Kragh’s ‘Homotopy Equivalence of Nearby Lagrangians and the Serre Spectral Sequence’”

May 21

4:00 pm

4:00 pm

Probability Seminar

Sequoia Hall Room 200

Sequoia Hall Room 200

Nike Sun (UC Berkeley)

“Spectral Algorithms for Tensor Completion” There is an unknown tensor, say an n x n x n array. We observe a small random subset of its entries, and wish to estimate the missing entries under a structural (low rank) assumption. Barak and Moitra (2015) gave an SDP algorithm for completion on n x n x n rank-r tensors (under some randomness assumptions) based on m >> n3/2r observed entries, with runtime O(n15).

“Spectral Algorithms for Tensor Completion” There is an unknown tensor, say an n x n x n array. We observe a small random subset of its entries, and wish to estimate the missing entries under a structural (low rank) assumption. Barak and Moitra (2015) gave an SDP algorithm for completion on n x n x n rank-r tensors (under some randomness assumptions) based on m >> n3/2r observed entries, with runtime O(n15).

May 22

12:30 pm

12:30 pm

Kiddie Colloquium

Math 383-N

Math 383-N

Joey Zou

“The Pompeiu Problem and Domains Supporting Overdetermined PDEs”

“The Pompeiu Problem and Domains Supporting Overdetermined PDEs”

May 22

4:00 pm

4:00 pm

Topology Seminar

Math 384-H

Math 384-H

Jesse Wolfson (UC Irvine)

“The Theory of Resolvent Degree, after Hamilton, Klein, Hilbert, and Brauer”

“The Theory of Resolvent Degree, after Hamilton, Klein, Hilbert, and Brauer”

May 23

12:30 pm

12:30 pm

Faculty Area Research

Math 384-H

Math 384-H

Jonathan Luk (Stanford)

“Weak Limits, Turbulence, and High Frequency Gravitational Waves” Suppose we have a partial differential equation and a sequence of solutions. Suppose moreover that the sequence of solutions converges to some limit in some weak sense. What can we say about the limit? I will discuss this question and how it relates to some problems arising in mathematical physics, including in fluid mechanics and general relativity.

“Weak Limits, Turbulence, and High Frequency Gravitational Waves” Suppose we have a partial differential equation and a sequence of solutions. Suppose moreover that the sequence of solutions converges to some limit in some weak sense. What can we say about the limit? I will discuss this question and how it relates to some problems arising in mathematical physics, including in fluid mechanics and general relativity.

May 24

4:30 pm

4:30 pm

Nike Sun (UC Berkeley)

“Phase Transitions in Random Constraint Satisfaction Problems” Assistant Professor Nike Sun will discuss random constraint satisfaction problems (CSPs). Broadly, these are large systems of variables subject to randomly generated constraints. Examples include random graph coloring problems and the random k-SAT problem. For a broad class of random CSP models, heuristic methods from statistical physics yield detailed predictions on a rich set of phase transitions and other phenomena, reminiscent of behaviors seen in models of spin glasses or disordered magnets.

“Phase Transitions in Random Constraint Satisfaction Problems” Assistant Professor Nike Sun will discuss random constraint satisfaction problems (CSPs). Broadly, these are large systems of variables subject to randomly generated constraints. Examples include random graph coloring problems and the random k-SAT problem. For a broad class of random CSP models, heuristic methods from statistical physics yield detailed predictions on a rich set of phase transitions and other phenomena, reminiscent of behaviors seen in models of spin glasses or disordered magnets.

May 25

3:00 pm

3:00 pm

Informal Geometry & Topology Seminar

Math 384-H

Math 384-H

Xuwen Zhu (Stanford)

“Realizability of Branched Covers and Spherical Cone Metrics” Every branched cover between Riemann surfaces is associated with its branching data, which satisfies certain combinatorics conditions. Hurwitz existence problem asks the question of whether all such data satisfying those constraints can be realized as a branched cover. We connect this problem to the recent development in spherical conical metrics, and give a new criterion of finding unrealizable branching data.

“Realizability of Branched Covers and Spherical Cone Metrics” Every branched cover between Riemann surfaces is associated with its branching data, which satisfies certain combinatorics conditions. Hurwitz existence problem asks the question of whether all such data satisfying those constraints can be realized as a branched cover. We connect this problem to the recent development in spherical conical metrics, and give a new criterion of finding unrealizable branching data.

May 25

3:00 pm

3:00 pm

Algebraic Geometry Seminar

Math 380-W

Math 380-W

Soren Galatius (Stanford)

“M_g, M_g^{trop}, GRT, and Kontsevich’s Complex of Graphs” I will report on recent joint work with Melody Chan and Sam Payne on the cohomology of M_g in degree 4g-6. It is known that the rational cohomology vanishes above this degree. We prove that the rational cohomology in this degree is non-trivial for all g \geq 7 and that its dimension grows faster than 1.324^g + constant, making it asymptotically larger than the entire tautological ring and disproving a recent conjecture of Church-Farb-Putman and an older conjecture of Kontsevich.

“M_g, M_g^{trop}, GRT, and Kontsevich’s Complex of Graphs” I will report on recent joint work with Melody Chan and Sam Payne on the cohomology of M_g in degree 4g-6. It is known that the rational cohomology vanishes above this degree. We prove that the rational cohomology in this degree is non-trivial for all g \geq 7 and that its dimension grows faster than 1.324^g + constant, making it asymptotically larger than the entire tautological ring and disproving a recent conjecture of Church-Farb-Putman and an older conjecture of Kontsevich.

May 25

4:15 pm

4:15 pm

Student Probability Research Seminar

Math 384-I

Math 384-I

Felipe Hernandez

“Multivariate Central Limit Theorems for Point Processes”

“Multivariate Central Limit Theorems for Point Processes”

May 25

4:30 pm

4:30 pm

Algebraic Geometry Seminar

Math 383-N

Math 383-N

Tathagata Basak (Iowa State University)

“A Complex Ball Quotient and the Monster” We shall talk about an arithmetic lattice M in PU(13,1) acting on the the unit ball B in thirteen dimensional complex vector space. Let X be the space obtained by removing the hypersurfaces in B that have nontrivial stabilizer in M and then quotienting the rest by M.

“A Complex Ball Quotient and the Monster” We shall talk about an arithmetic lattice M in PU(13,1) acting on the the unit ball B in thirteen dimensional complex vector space. Let X be the space obtained by removing the hypersurfaces in B that have nontrivial stabilizer in M and then quotienting the rest by M.

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