MATH 663
Geometry of Metric Spaces
Spring 2016
Instructor: Florent Baudier
Office: Blocker 525C
Office hours: by appointment
   ***Tuesday 04/26 class will meet at 5pm in BLOC 506A.***
Lectures: Tuesday 3:55-5:10 p.m., Blocker 120
Thursday 1-2:15 p.m., Blocker 605AX
Textbook: no textbook is required but the following material will be useful for the course

J. Matoušek, Lectures on Discrete Geometry, Graduate Texts in Mathematics, Springer, 2002.
J. Matoušek, Lectures notes on metric embeddings.
P. Nowak and G. Yu, Large Scale Geometry, EMS Textbooks in Mathematics, European Mathematical Society (EMS), Zurich, 2012.
M. I. Ostrovskii, Metric Embeddings, De Gruyter Studies in Mathematics, vol. 49, De Gruyter, Berlin, 2013.
Schedule
Date of Class Material covered
01/19 lecture 1: the one about the cut cone decomposition of L1-metrics.
Most of the material covered was taken from section 3 in A. Naor's ICM article.
01/21 lecture 2: the one about integrality gaps of the Sparsest Cut Problem
Most of the material covered was taken from sections 4.1 4.2, 4.3 in A. Naor's ICM article.
01/26 lecture 3: the one about scale maps with deficiency
01/28 lecture 4: the one about J. Lee's gluing technique
Most of the material can be found in M. Ostrovskii's book, section 3.4.
02/02 lecture 5: the one about Bourgain's embedding method
Most of the material can be found in M. Ostrovskii's book, section 3.4.
02/04 lecture 6: the one about stochastic padded decompositions
Most of the material can be found in M. Ostrovskii's book, section 3.4.
02/09 lecture 7: the one about the combinatorial definition of expander graphs
Most of the material can be found in M. Ostrovskii's book, section 4.2.
02/11 lecture 8: the one about the spectral characterization of expander graphs
Most of the material can be found in Nowak and Yu's book, section 5.6. The introductory chapter of Davidoff-Sarnak-Valette book is an excellent introduction to the speactral aspect of expander graphs.
02/16 lecture 9: the one about Matoušek's extrapolation technique
The presentation of Matoušek's extrapolation technique follows closely the original argument of Matoušek.
02/18 lecture 10: the one about dimension reduction in L2
The presentation of the Johnson-Lindenstrauss dimension reduction was mostly taken from Matoušek's article on this topic.
02/23 lecture 11: the one about the impossibility of dimension reduction in L1
The proof of the Brinkman-Charikar theorem on the impossibility of dimension reduction in L1 was taken from Krauthgamer-Lee-Naor article and uses the Laakso graphs of Lang and Plaut.
Two proofs of the crucial but classical uniform convexity inequality in Lp (see the Ball-Carlen-Lieb article for the original proofs and a historical account of the inequality) can be found on A. Naor's webpage (A. Naor's take and J. Matoušek's take).
02/25 lecture 12: the one about the Euclidean distortion of the Hamming cubes and the introduction to the Ribe progam
A good reference for the Euclidean distortion of the Hamming cubes is Matoušek's lecture notes section 3.4.
As far as the Ribe program is concerned I suggest the following excellent readings: K. Ball's Bourbaki Seminar and A. Naor's 10th Takagi Lectures.
The class will meet from 1pm to 2:15pm this Thursday in BLOC 220 to avoid a conflict with the Noncommutative Geometry Colloquium of N. Higson.
03/01 lecture 13: the one about metric characterizations of the superreflexive class in terms of graph preclusions: binary trees (embeddability issue)
03/03 class canceled; we will make it up by extending a bit a few subsequent lectures
03/08 lecture 14: the one about metric characterizations of the superreflexive class in terms of graph preclusions: binary trees (non-embeddability issue)
03/10 lecture 15: the one about metric characterizations of the superreflexive class in terms of graph preclusions: fractal built graphs
03/22 lecture 16: the one about local-to-global theorems and their applications
03/24 lecture 17: the one about the barycentric gluing technique
03/29 lecture 18: the one about Rolewicz property (β) and the distortion of ω-regular trees
03/31 lecture 19: the one about snowflake exponents and compression exponents
04/05 lecture 20: the one about Kalton-Randrianarivony inequality
04/07 lecture 21: the one about the large scale geometry of groups and the Milnor-Svarc lemma
The material from this lecture can be found in Nowak-Yu chapter 1.
04/12 lecture 22: the one about proper affine isometric actions and equivariant embeddings
The material from this lecture can be found in Nowak-Yu chapter 6
04/14 lecture 23: the one about equivariant embeddability of the Heisenberg group into ergodic spaces
The material from this lecture is extracted for the article of a Austin, Tessera and Naor.
04/19 class canceled; we will make it up by extending a bit the remaining lectures
04/21 lecture 24: the one about equivariant embeddings of amenable groups
The material from this lecture can be found in Bemyamini-Lindenstrauss chapter 8
04/26 lecture 25: the one about compression exponents and the speed of random walks: the equivariant setting
Class will meet at 5pm in BLOC 506A. The material from this lecture is extracted from the article of Naor and Peres.
04/28 lecture 26: the one about compression exponents and the speed of random walks: the non-equivariant setting
The material from this lecture is extracted from the article of Austin, Naor and Peres.