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PRODID:-//Mathematics Department//NONSGML mathical.php//EN
X-WR-CALNAME:Mathematics Department
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be5142d4@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220421T121500
CATEGORIES:Topology Seminar
SUMMARY:Adria Marin Salvador: On the contact manifold of null
geodesics of a spacetime
DESCRIPTION:Abstract: The space of null geodesics of a spacetime (a
Lorentzian manifold\n with a choice of future) sometimes has the
structure of a smooth manifold. When this is the case\, \nit comes
equipped with a canonical contact structure. In this talk I will
show that this is the case for the family of spacetimes \n{(S2×S1\,
go-dt2/c2)}c∈N+\, with go \nthe round metric on S2 and t the
S1-coordinate. Their spaces of null geodesics are actually the lens
spaces \nL(2c\,1) together with the pushforward of the canonical
contact structure on STS2≅L(2\,1) under the natural projection
\nL(2\,1)→L(2c\,1). These results can also be extended to trivial
bundles over Zoll manifolds. On the other hand\, motivated by these
\nexamples\, I will comment on how Engel geometry can be used to
describe the manifold of null geodesics of a certain class of
\nthree-dimensional spacetimes\, by considering the Cartan
deprolongation of their Lorentz prolongation\, and how this gives an
idea on \nhow to retrieve the spacetime from its contact manifold of
null geodesics. This is joint work with F. Presas and R. Rubio.
LOCATION:Zoom\, please ask Vladimir Chernov for the login
information
URL:https://math.dartmouth.edu/~topology/
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be5143f9@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220425T160000
CATEGORIES:Logic Seminar
SUMMARY:TBA: TBA
LOCATION:Kemeny 307
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be5144ad@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220426T143000
DTEND;TZID=America/New_York:20220426T153000
CATEGORIES:Algebra and Number Theory Seminar
SUMMARY:Eran Assaf: Modular forms and where to find them - the case
of rank four
DESCRIPTION:We consider spaces of modular forms attached to positive
definite quadratic forms in four variables\, and make explicit their
connection to Hilbert modular forms using the even Clifford functor.
By relating it to the theory of theta lifts we obtain an explicit
theta correspondence\, and gain a full understanding of the systems
of Hecke eigenvalues that can arise. This is joint work with Dan
Fretwell\, Colin Ingalls\, Adam Logan\, Spencer Secord and John
Voight.
LOCATION:Kemeny 343
URL:https://math.dartmouth.edu/~zahlen/
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514572@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220502T160000
CATEGORIES:Logic Seminar
SUMMARY:Justin Miller: postponed to next week
LOCATION:Kemeny 307
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be51461f@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220503T100000
DTEND;TZID=America/New_York:20220503T110000
CATEGORIES:Combinatorics Seminar
SUMMARY:Susanna Fishel: Maximal chains in certain bond lattices
DESCRIPTION:Both the noncrossing partition/Kreweras lattice and
parking functions are well-studied objects in combinatorics. In 1997
Richard Stanley found a bijection between the maximal chains in the
lattice and parking functions. We investigated what happens under
the bijection when we restrict to certain induced sublattices\, and
enumerated maximal chains in those cases. Joint with Shreya
Ahirwar\, Parikshita Gya\, Pamela E. Harris\, Nguyen (Emily) Pham\,
Andrés R. Vindas-Meléndez\, and Dan Khanh (Aurora) Vo.\n\n
Meeting ID: 954 4736 6763\n Passcode: Catalan#\n
https://dartmouth.zoom.us/j/95447366763?pwd=ZFk5OElEVkdadFVXMEg1QlVOaHhnQT09\n
LOCATION:Virtual
URL:math.dartmouth.edu/~comb
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be5146f6@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220503T153000
DTEND;TZID=America/New_York:20220503T163000
CATEGORIES:Algebra and Number Theory Seminar
SUMMARY:Asher Auel: Unramified cohomology of products of elliptic
curves
DESCRIPTION:The unramified cohomology of an algebraic variety is\,
in degree 1 and 2\, related to torsion in the Néron-Severi group
and the Brauer group\, and in degree 3\, to the integral Hodge
conjecture for codimension 2 cycles. Gabber proved that over the
complex numbers\, the product of elliptic curves with algebraically
independent j-invariants has nontrivial unramified cohomology in top
degree. I’ll explain joint work with V. Suresh extending such a
result to products of elliptic curves over the rational numbers\,
and more generally\, to fields admitting a nontrivial discrete
valuation. In particular\, this leads to an amusing open problem
where elliptic curves whose j-invariants are certain algebraic units
cause the most difficulty.
LOCATION:Kemeny 343
URL:https://math.dartmouth.edu/~zahlen/
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be5147c3@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220504T180000
CATEGORIES:⋆ Kemeny Lecture ⋆
SUMMARY:Anna Gilbert: CANCELED - Combinatorial group testing designs
and algorithms: pooled testing for biological applications
DESCRIPTION:Abstract: \n\nSince the beginning of the COVID-19
pandemic\, there has been considerable interest and discussion in
both the popular media and the scientific/medical literature on
pooled testing for COVID. Indeed\, in June 2020\, the FDA released
guidelines on pooled testing procedures that are now available to
diagnostic laboratories. \n\nPooled testing\, as described in the
popular press and the FDA's ruling\, is one model for combinatorial
group testing. In this talk\, I will discuss a variety of
mathematical models for combinatorial group testing\, including the
design of both the pooling matrix and the decoding algorithms. I
will cover major mathematical and algorithmic results in
combinatorial group testing and then address what these mathematical
results have to say about the practical application of pooled
testing. The mathematical tools span a variety of areas from error
correcting codes to expander graphs. As with many scientific and
technological endeavors\, the gap between theory and practice is
enormous. (While many of the popular press articles detailed the
origins of combinatorial group testing\, many left out that it was
never actually used in its original form!) On a more positive note\,
I will give some examples of where combinatorial group testing is
used in "theory applications."
LOCATION:100 Life Sciences Center (Oopik Auditorium)
URL:https://math.dartmouth.edu/activities/kemeny-lectures/2022-Gilbert.php
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514898@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220505T151500
CATEGORIES:⋆ Kemeny Lecture ⋆
SUMMARY:Anna Gilbert: CANCELED - Sparse Fourier Transform: really
fast Fourier transform
DESCRIPTION:The Discrete Fourier Transform (DFT) is a
fundamental\ncomponent of numerous computational techniques in
signal processing\nand scientific computing. The most popular means
of computing the DFT\nis the Fast Fourier Transform (FFT). However\,
with the emergence of\nbig data problems\, in which the size of the
processed data sets can\neasily exceed terabytes\, the “Fast” in
Fast Fourier Transform is often\nno longer fast enough. In
addition\, in many big data applications it\nis hard to acquire a
sufficient amount of data in order to compute the\ndesired Fourier
transform in the first place. The Sparse Fourier\nTransform (SFT)
addresses the big data setting by computing a\ncompressed Fourier
transform using only a subset of the input data\, in\ntime
sub-linear in the data set size. The goal of this talk is to\nsurvey
these recent developments\, to explain the basic techniques
with\nexamples and applications in big data\, to demonstrate
trade-offs in\nempirical performance of the algorithms\, and to
discuss the connection\nbetween the SFT and other techniques for
massive data analysis such as\nstreaming algorithms and compressive
sensing.
LOCATION:007 Kemeny
URL:https://math.dartmouth.edu/activities/kemeny-lectures/2022-Gilbert.php
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514970@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220506T151500
CATEGORIES:⋆ Kemeny Lecture ⋆
SUMMARY:Anna Gilbert: CANCELED - Metric representations: Algorithms
and Geometry
DESCRIPTION:Given a set of distances amongst points\, determining
what metric representation is most “consistent” with the input
distances or the metric that best captures the relevant geometric
features of the data is a key step in many machine learning
algorithms. In this talk\, we discuss a number of variants of this
problem\, from convex optimization problems with metric constraints
to sparse metric repair.
LOCATION:307 Kemeny
URL:https://math.dartmouth.edu/activities/kemeny-lectures/2022-Gilbert.php
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514a2b@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220509T160000
CATEGORIES:Logic Seminar
SUMMARY:Justin Miller: TBA
LOCATION:Kemeny 307
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514ad3@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220510T100000
DTEND;TZID=America/New_York:20220510T110000
CATEGORIES:Combinatorics Seminar
SUMMARY:Ben Adenbaum: r-rowmotion
DESCRIPTION:Abstract: Rowmotion is a classical action on
antichains/order ideals of a poset. This map and its generalizations
as well as the concept of homomesy\, where a statistic has constant
average over the orbits of an action\, are frequently studied in
Dynamical Algebraic Combinatorics. We will discuss a new
generalization of rowmotion\, which we call r-rowmotion\, and some
associated homomesies. Additionally\, we discuss how r-rowmotion
relates to other generalizations of rowmotion and some combinatorial
consequences. This is joint work with Sergi Elizalde.\n\nWe will go
for lunch after the talk.
LOCATION:Kemeny 307
URL:math.dartmouth.edu/~comb
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514b92@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220510T143000
DTEND;TZID=America/New_York:20220510T153000
CATEGORIES:Algebra and Number Theory Seminar
SUMMARY:Andrew Hanlon: Relating linking disks and toric Frobenius
via homological mirror symmetry
DESCRIPTION:We will give an example-based overview of one approach
to homological mirror symmetry for toric varieties. An emphasis will
be placed on the implications for the structure of the derived
categories of toric varieties coming from identifying a canonical
generating set of objects. This talk is based on joint work with
Jeff Hicks.
LOCATION:Kemeny 343
URL:https://math.dartmouth.edu/~zahlen/
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514c4b@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220510T160000
CATEGORIES:Geometry Seminar
SUMMARY:Alena Erchenko: Riemannian Anosov extensions and
applications
DESCRIPTION:ABSTRACT: Consider a smooth Riemannian manifold
$\\Sigma$ with strictly convex spherical boundary\, hyperbolic
trapped set (possibly empty)\, and no conjugate points. We show that
$\\Sigma$ can be isometrically embedded with codimension $0$ into a
closed Riemannian manifold with Anosov geodesic flow. We will
demonstrate how to apply our result to prove marked lens rigidity in
a conformal class. We will also explain one of the main
ingredients\, which is the analysis of the behavior of Jacobi
fields\, and the ideas in the proof of the theorem. This is joint
work with Dong Chen and Andrey Gogolev.
LOCATION:Kemeny 008
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514d0c@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220512T151500
CATEGORIES:Math Colloquium
SUMMARY:Tye Lidman: Cosmetic crossings and knots
DESCRIPTION:The structure of a knotted loop in three-space can be
analyzed by how two strands cross over or under each other. In this
talk we will discuss the "Nugatory Crossing Conjecture'' which
posits that changing pretty much any over-crossing to an
under-crossing or vice versa fundamentally changes the knot. This is
joint work with Artem Kotelskiy\, Allison Moore\, Liam Watson\, and
Claudius Zibrowius. This talk will be accessible to graduate
students (and many undergraduates).
LOCATION:041 Haldeman
URL:https://math.dartmouth.edu/calendar/agenda-colloq.php
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514dda@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220516T160000
CATEGORIES:Logic Seminar
SUMMARY:TBA: TBA
LOCATION:Kemeny 307
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514e82@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220517T100000
DTEND;TZID=America/New_York:20220517T110000
CATEGORIES:Combinatorics Seminar
SUMMARY:Carl Pomerance: Coprime permutations
DESCRIPTION:It is convenient to think of permutations of finite sets
as\npermuting [n]\, the first n positive integers. Since we also
do\narithmetic with these numbers\, it seems natural to combine the
two\nand consider permutations with arithmetic constraints. An
interesting\npaper from 1983 of Erdos\, Freud\, and Hegyvari did
just this\, and\nthere are several other papers in the literature\,
including one of\nJackson from 1977. In this talk I'll describe
some recent work on the\nenumeration problem of those permutations
of [n] where corresponding\nnumbers are relatively prime\, and some
other similar problems.\n\nMeeting ID: 954 4736 6763\nPasscode:
Catalan#\nhttps://dartmouth.zoom.us/j/95447366763?pwd=ZFk5OElEVkdadFVXMEg1QlVOaHhnQT09
LOCATION:Kemeny 307 and Zoom
URL:https://math.dartmouth.edu/~comb
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be514f5f@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220517T143000
DTEND;TZID=America/New_York:20220517T153000
CATEGORIES:Algebra and Number Theory Seminar
SUMMARY:Sarah Frei: Obstructions to rationality for conic bundle
threefolds
DESCRIPTION:To show that a variety is not rational\, one must
exhibit some birational invariant – a so-called obstruction to
rationality – that is trivial for projective space and nontrivial
for the given variety. The intermediate Jacobian is an obstruction
to rationality in dimension 3\, first introduced over the complex
numbers by Clemens–Griffiths to show that cubic threefolds are
irrational. Hassett–Tschinkel and Benoist–Wittenberg recently
refined the intermediate Jacobian obstruction over non-closed fields
by introducing an intermediate Jacobian torsor (IJT) obstruction. In
joint work with L. Ji\, S. Sankar\, B. Viray\, and I. Vogt\, we
identify the torsors arising in the IJT obstruction for conic bundle
threefolds over P^2\, and use this information to show that the IJT
obstruction does not determine rationality in the case of conic
bundle threefolds with degree 4 discriminant locus.
LOCATION:Kemeny 343
URL:https://math.dartmouth.edu/~zahlen/
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be515063@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220519T151500
CATEGORIES:Math Colloquium
SUMMARY:Bohan Zhou: Efficient and Exact Multimarginal Optimal
Transport with Pairwise Costs
DESCRIPTION:Optimal transport has profound and wide applications
since its introduction in 1781 by Monge. Thanks to the
Benamou-Brenier formulation\, it provides a meaningful functional in
the image science like image and shape registrations. However\,
exact computation through LP or PDE is in general not practical in
large scale\, while the popular entropy-regularized method
introduces additional diffusion noise\, deteriorating shapes and
boundaries. Until the recent work [Jacobs and Leger\, A Fast
Approach to Optimal Transport: the back-and-forth method\,
Numerische Mathematik\, 2020]\, solving OT in a both accurate and
fast fashion finally becomes possible. Multiple marginal optimal
transport is a natural extension from OT but has its own interest
and is in general more computationally expensive. The entropy method
suffers from both diffusion noise and high dimensional computational
issues. In this work with Matthew Parno\, we extend from two
marginals to multiple marginals\, on a wide class of cost functions
when those marginals have a graph structure. This new method is fast
and does not introduce diffusion. As a result\, the new proposed
method can be used in many fields those require sharp boundaries. If
time allows\, we will illustrate by examples the faithful joint
recover via MMOT of images with sharp boundaries\, with applications
on sea ice prediction.\n
LOCATION:041 Haldeman
URL:https://math.dartmouth.edu/calendar/agenda-colloq.php
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be515139@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220523T160000
CATEGORIES:Logic Seminar
SUMMARY:TBA: TBA
LOCATION:Kemeny 307
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be5151e2@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220524T100000
DTEND;TZID=America/New_York:20220524T110000
CATEGORIES:Combinatorics Seminar
SUMMARY:Bruce Sagan: Stirling numbers in type B
DESCRIPTION:The ordinary Stirling numbers count set partitions and
permutations of {1\, 2\, ...\, n} by number of blocks and number of
cycles\, respectively. These mpermutations are the ones in the
symmetric group which is the Coxter group of type A. We introduce
versions of these numbers and their q-analogues for the
hyperoctahedral group which is the Coxeter group of type B. We will
discuss various interesting identities\, connections with symmetric
functions\, Möbius functions of posets\, and Hilbert series for
coinvariant algebras. This is joint work with Joshua Swanson.\n\nThe
talk will be followed by a 20-minute chat with the
speaker.\n\n\nMeeting ID: 954 4736 6763\nPasscode:
Catalan#\nhttps://dartmouth.zoom.us/j/95447366763?pwd=ZFk5OElEVkdadFVXMEg1QlVOaHhnQT09
LOCATION:Virtual
URL:https://math.dartmouth.edu/~comb
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be5152a4@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220524T143000
DTEND;TZID=America/New_York:20220524T153000
CATEGORIES:Algebra and Number Theory Seminar
SUMMARY:Tristan Phillips: Counting Elliptic Curves Over Number
Fields
DESCRIPTION:A famous result of Mazur classifies the possible torsion
subgroups of an elliptic curve over the rational numbers. It is then
natural to ask how frequently each of these torsion subgroups occur?
More generally\, one can ask\, how frequently do elliptic curves
with a given level structure occur? Recently there have been many
results addressing this question by giving asymptotics for the
number of elliptic curves of bounded height with a prescribed level
structure. Most of these results have been over the rational
numbers. In this talk I will discuss how one can extend many of
these results to arbitrary number fields.
LOCATION:Kemeny 343
URL:https://math.dartmouth.edu/~zahlen/
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be515375@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220530T160000
CATEGORIES:Logic Seminar
SUMMARY:TBA: TBA
LOCATION:Kemeny 307
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be515420@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220531T100000
DTEND;TZID=America/New_York:20220531T110000
CATEGORIES:Combinatorics Seminar
SUMMARY:Rosa Orellana: TBD
LOCATION:Kemeny 307
URL:https://math.dartmouth.edu/~comb
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be5154cc@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220531T143000
DTEND;TZID=America/New_York:20220531T153000
CATEGORIES:Algebra and Number Theory Seminar
SUMMARY:Ajmain Yamin: TBA
LOCATION:Kemeny 343
URL:https://math.dartmouth.edu/~zahlen/
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be51557f@math.dartmouth.edu
DTSTART;TZID=America/New_York:20220607T143000
DTEND;TZID=America/New_York:20220607T153000
CATEGORIES:Algebra and Number Theory Seminar
SUMMARY:Jack Petok: TBA
LOCATION:Kemeny 343
URL:https://math.dartmouth.edu/~zahlen/
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be515629@math.dartmouth.edu
DTSTART;TZID=America/New_York:20221012T180000
CATEGORIES:∾ Prosser Lecture ∾
SUMMARY:Mark Levi: TBA
LOCATION:TBA
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20220521T224701Z
UID:20220521T18470162896be5156d2@math.dartmouth.edu
DTSTART;TZID=America/New_York:20221013T151500
CATEGORIES:Math Colloquium
SUMMARY:Mark Levi: TBA
LOCATION:TBA
END:VEVENT
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