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Seminars and Colloquiums
for the week of February 18, 2019


Ryan Unger, University of Tennessee
Shuler Hopkins and Tamara Riggs, University of Tennessee
Householder Lecture - ORNL Weinberg Auditorium
Huy Nguyen, Brown University
Michael Kirby, Colorado State University

3:00 PM – 3:30 PM
Monday, Tuesday & Wednesday
Room: Ayres 401
Hosted by: Jacob Dennerlein and Jesse Sautel

Topics: How to stay on track with your research/how to quantify progress; things to expect before, during, and after an oral exam; weekly check-in (a time for students and faculty to discuss the current happenings of the Mathematics Department and share any concerns or ideas).

Monday, 2/18

TITLE: Introduction to Ricci flow with bubbling off
SPEAKER: Ryan Unger, University of Tennessee
TIME: 3:35 PM-5:30 PM
ROOM: Ayres 113
In this talk I will introduce a “simpler” surgery procedure due to Bessieres-Besson-Boileau-Maillot-Porti where the surgery takes place before the singular time. This is more reminiscent of Hamilton’s original vision and avoids some technical details with the ends of the regular set.

In any remaining time I will start discussing finite time extinction for irreducible non-aspherical manifolds under Ricci flow with bubbling off.

Wednesday, 2/20

TITLE: Counting bi-unimodular sequences of prime length. 
SPEAKER: Shuler Hopkins and Tamara Riggs, University of Tennessee
TIME: 2:30 PM-3:20 PM
ROOM: Ayres 113
An old question of Enflo asks to classify all complex-valued functions f on {0,1,…,n-1}, such that both f and its Fourier transform are unimodular. Such maps, which we will refer to as bi-unimodular sequences, can also be described in terms of circulant Hadamard matrices.  We present a paper of Haagerup which counts the number of bi-unimodular sequences of prime length.  

TITLE: Communication-avoiding Algorithms for Linear Algebra, Machine Learning and Beyond
SPEAKER: James Demmel, University of California, Berkeley
TIME: 3:30 PM-4:30 PM
ROOM: ORNL Weinberg Auditorium (4500-N)
Abstract: Algorithms have two costs: arithmetic and communication, i.e. moving data between levels of a memory hierarchy or processors over a network. Communication costs (measured in time or energy per operation) already greatly exceed arithmetic costs, and the gap is growing over time following technological trends. Thus our goal is to design algorithms that minimize communication. We present new algorithms that communicate asymptotically less than their classical counterparts, for a variety of linear algebra and machine learning problems, demonstrating large speedups on a variety of architectures. Some of these algorithms attain provable lower bounds on communication. We describe a generalization of these lower bounds and optimal algorithms to arbitrary code that can be expressed as nested loops accessing arrays, assuming only that array subscripts are affine functions of the loop indices, a special case being convolutional neural nets.

Biography: James Demmel is the Dr. Richard Carl Dehmel Distinguished Professor of Computer Science and Mathematics at the University of California at Berkeley, and Chair of the EECS Department. His research is in numerical linear algebra, HPC, and communication avoiding algorithms. He is known for his work on the LAPACK and ScaLAPACK linear algebra libraries. He is a member of the NAS, NAE, and American Academy of Arts and Sciences; a Fellow of the AAAS, ACM, AMS, IEEE and SIAM; and winner of the IPDPS Charles Babbage Award, IEEE Computer Society Sidney Fernbach Award, the ACM Paris Kanellakis Award, and numerous best paper prizes.

Students and faculty must have a visitor badge to attend the talk.

Thursday, 2/21

TITLE: On global stability of optimal rearrangement maps
SPEAKER: Huy Nguyen, Brown University
TIME: 2:10 PM-3:25 PM
ROOM: Ayres 114

See PDF for abstract.

Friday, 2/22

SPEAKER: Michael Kirby, Colorado State University
TIME: 11:15 AM-12:05 PM
ROOM: Ayres 401
We have been discussing the paper by Michael Kirby and his co-authors Tomojit Ghosh and Xiaofeng Ma titled "New Tools for the Visualization of Biological Pathways" (published in Methods 132 (2018) pgs. 26-33).  During this week's seminar, we host a visit by co-author Michael Kirby from Colorado State University (Departments of Mathematics and Computer Science) to discuss this work in person. Following a brief introduction of the main ideas of the work by Dr. Kirby, graduate students Ibrahim Aslan and Shelby Scott will moderate the discussion with the group.  If you are interested in being added the Math Biology Seminar 'BaseCamp' site to receive notices and seminar materials directly, please contact Judy Day at  


If you are interested in giving or arranging a talk for one of our seminars or colloquiums, please review our calendar.

If you have questions, or a date you would like to confirm, please contact

Past notices:

Feb 11, 2019

Feb. 4, 2019

Jan. 28, 2019

Jan. 21, 2019

Jan. 7, 2019

Winter Break

Dec. 10, 2018

Dec. 3, 2018

Nov. 26, 2018

Nov. 19, 2018

Nov. 12, 2018

Nov. 5, 2018

Oct. 29, 2018

Oct. 22, 2018

Oct. 15, 2018

Oct. 8, 2018

Oct. 1, 2018

Sept. 24, 2018

Sept. 17, 2018

Sept. 10, 2018

Sept. 3, 2018

Aug. 27, 2018



last updated: February 2019

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