Department of

# Mathematics

Seminar Calendar
for events the day of Friday, September 17, 2021.

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events for the
events containing

Questions regarding events or the calendar should be directed to Tori Corkery.
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Friday, September 17, 2021

2:00 pm in 347 Altgeld Hall,Friday, September 17, 2021

#### Heuristics and LIES

###### Ryan McConnell (UIUC)

Abstract: In this talk I will discuss several heuristics used in determining "optimal" ranges for well-posedness in dispersive PDEs, which will include several methods for disproving well-posedness. I will then rant about how, much like statistics, people use these heuristics to LIE to their unsuspecting readers. As always, there will be cookies.

4:00 pm in Altgeld Hall 347,Friday, September 17, 2021

#### Lie Groups of Diffeomorphisms

###### Wilmer Smilde (UIUC)

Abstract: The diffeomorphism group of a smooth manifold is really large, yet it is still possible to make sense of it as an infinite-dimensional Lie group. Things get more complicated when we look at subgroups preserving geometric structures. In this talk we will look at a few things: the smooth structure on the group of diffeomorphisms that makes it into a Lie group; subgroups preserving several geometric structures, such as metrics, complex structures, symplectic structures; how Lie groupoids can be used to describe the symmetries of several "intransitive" geometric structures, such as manifolds with a distinguished hypersurface (e.g. a boundary) and foliations. The main focus is on the geometry, so no technical knowlegde of infinite-dimensional manifolds is required. Also, Lie groupoids will only be used at the very end to provide context to some examples, so no worries if you have never seen them before. Hope to see many of you on Friday!