### PhD Defense

^{2}(G) and is an isometry, we call this a continuous wavelet transform and that psi is a continuous wavelet or admissible for tau. We will give a general Calderon condition for when such admissible vectors exist given some assumptions on N. Then, we will explicitly construct and decompose the quasi-regular representation on the class of odd degree oscillator groups and use this to show that G admits no admissible vectors but the dilated group G

_{d}does.

### Sage Days 104: Arithmetic Dynamics

November 17-20. BSC Room 254.

This 4-day workshop includes a combination of mathematical talks, Sage tutorials, and Sage development. The main goal is to promote and improve the dynamical systems functionality in Sage and to expand the scope of the database of dynamical systems. Users new to Sage and Sage development are welcome. There is no initial knowledge needed, everyone is welcome whether they are new Sage learners or Sage expert. We believe in diversity in backgrounds and experiences.

For details, visit the workshop website at: https://wiki.sagemath.org/days104

### Master's Thesis Defense

Nick Simone, SLU

A Score Minimizing Vertex Partitioning Algorithm using Simulated Annealing

Thursday, November 21 at 9:30am in Ritter 334.

### Colloquium

Courtney Paquette, Google Brain, Montreal

Friday, November 15 at 4:00pm in Ritter 242 with refreshments beforehand in the Ritter Hall Lobby.

Title: Algorithms for stochastic nonconvex and nonsmooth optimization

Abstract:

Machine learning has introduced new optimization challenges with its use of nonconvex losses, noisy gradients, and statistical assumptions. While convergence guarantees in the deterministic, convex settings are well-documented, algorithms for solving large-scale nonsmooth and nonconvex problems remain in their infancy.

I will begin by isolating a class of nonsmooth and nonconvex functions that can be used to model a variety of statistical and signal processing tasks. Standard statistical assumptions on such inverse problems often endow the optimization formulation with an appealing regularity condition: the objective grows sharply away from the solution set. We show that under such regularity, a variety of simple algorithms converge rapidly when initialized within constant relative error of the optimal solution. We illustrate the theory and algorithms on the real phase retrieval problem, and survey a number of other applications, including blind deconvolution and covariance matrix estimation.

One of the main advantages of smooth optimization over its nonsmooth counterpart is the potential to use a line-search for improved numerical performance. A long-standing open question is to design a line-search procedure in the stochastic setting. In the second part of the talk, I will present a practical line-search method for smooth stochastic optimization that has rigorous convergence guarantees and requires only knowable quantities for implementation.

### Colloquium

Khazhak Navoyan, University of Mississippi Oxford

Friday, November 1 at 4:00pm in Ritter 242 with refreshments beforehand in the Ritter Hall Lobby.

Title: **The positive Schur property on spaces of regular multilinear operators**

Abstract: In this paper we give necessary and sufficient conditions for the space of regular multilinear operators from the product of Banach lattices to a Dedekind complete Banach lattice to have the positive Schur property. We also characterize the positive Schur property on the positive projective n-fold tensor product of Banach lattices, n ε N, and on its dual.

### Algebra Seminar

Katie Radler and Sarah Aljohani, SLU graduate students

A weekly series of talks, Tuesday, September 24 - Tuesday, October 15 at 11:00am in Ritter 229.

**Variations of prime ideals and factorization of ideals in Leavitt path algebras**

### Colloquium

Salman Parsa, SLU

Friday, October 11 at 4:00pm in Ritter 242 with refreshments beforehand in the Ritter Hall Lobby.

**Obstructions to embedding the join of two simplicial complexes in Euclidean spaces**

The problem of embedding (i.e., mapping continuously and injectively) a simplicial complex of dimension d into a Euclidean space of dimension 2d is a generalization of the problem of drawing a graph on a plane. When d>2, there exists a complete homological obstruction for deciding the embeddability of a complex into 2d space. This is called the van Kampen obstruction. We discuss this concept and state and explain new results that enable us to decide the vanishing of the van Kampen obstruction of the join of two complexes based on the obstruction classes of the factors.

### Colloquium

Charles Burnette, SLU

Friday, September 20 at 4:00pm in Ritter 242 with refreshments beforehand in the Ritter Hall Lobby.

**Title: Involution factorizations of Ewens random permutations**

Abstract: An involution is a permutation that is its own inverse. Given a permutation σ of [n], let invol_{n}(σ) denote the number of ways to express σ as a composition of two involutions of [n]. The random variables invol_{n} are asymptotically lognormal when the symmetric groups S_{n} are each equipped with Ewens Sampling Formula probability measures of some fixed positive parameter θ. In this talk, I will summarize what is already known and explain new results about the previously determined limiting distribution of invol_{n} for uniform random permutations, i.e. the specific case of θ = 1.

### PhD Defense: Christopher Halverson

Gradient Young Measures and Maps of Exponentially Integrable Distortion

Abstract: We aim to extend the relationship established by Astala and Faraco between functions of bounded distortion and gradient Young measures to the more general setting of maps of exponentially integrable distortion. We will do this using techniques derived from singular operator theory.

Ritter Hall 229 at 10am on July 29th

### Departmental Awards Ceremony

Friday, April 26 in Lee Lecture Hall. Refreshments at 4:00pm. Ceremony begins at 4:20pm.

Featuring the 2019 Case Lecture by Dr. Liberty Vittert, Washington University in St. Louis

**How to win the lottery and get away with murder**

Abstract: Data, numbers statistics are coming at us like a hurricane, it can be completely overwhelming. This influx of data means that government, media, businesses, advertisers, and even scientists will be using data and numbers to sway your opinion, rightly and wrongly. With enormous amounts of information we run the risk of misinformation and even more worrisome disinformation. Using real-life examples and good old common sense, we are going to learn what questions we should be asking of data in order to spot the lies, damned lies, and statistics (with a little fake news thrown in there for good measure).

### Colloquium

K. M. Rangaswamy, University of Colorado, Colorado Springs

*Wednesday*, April 3, at 4:10pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

Title:** Are Leavitt path algebras really commutative algebras in non-commutative clothing?**

Abstract: Leavitt path algebras of directed graphs over a field are algebraic analogues of graph C*-algebras of operators on Hilbert spaces. This talk is a report on some of the recent investigations illustrating two essential features of these algebras. The first makes the Leavitt path algebras really useful tools in constructing examples of rings of various types. The second is about the ideal lattice of Leavitt path algebras, which seems to posess similarities with commutative rings. Various graphical constructions will illustrate these conclusions.

### Algebra Seminar

Steve Szabo, Eastern Kentucky University

Thursday, April 4, 10:00-10:50am in Ritter 225

Title: **Minimal Reversible Nonsymmetric Rings and other Related Minimal Rings**

Abstract:

In a paper by Marks on the taxonomy of 2-primal rings, examples of various types of rings that are related to 2-primal rings such as reduced, symmetric, duo, reversible and PS I were given in order to show that the ring class inclusions were strict. In this talk, this taxonomy is refined to include NI, abelian and reflexive rings. Then minimal examples of all ring types possible are provided. In particular, it is shown that the F_2 algebra over Q_8 is a minimal reversible nonsymmetric ring answering a question by Marks on such rings. Finally, connections to minimal abelian reflexive nonsemicommutative rings are also discussed.

### Colloquium

William Yslas Vélez, University of Arizona

Friday, April 5, at 4:10pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

**Increasing the mathematical content of the undergraduate curriculum for all students. Good for the student. Good for the university.**

Abstract: In the late 1980’s I began my efforts to increase the success rate of minorities in first semester calculus. These minority students came from all majors, though most were in engineering. The interventions that I devised were very time consuming and as the number of minority students increased, I could not manage that kind of effort. I developed my Calculus Minority Advising Program in an effort to meet with scores of minority students each semester. This program consists of a twenty-minute meeting with each student at the beginning of each semester. The meetings with the students eventually transformed my own attitude about the importance of mathematics in their undergraduate curriculum. It sloooowly dawned on me. The more mathematics a student took, the more opportunities were available to that student.

I took over the position of Associate Head for Undergraduate Affairs in the department in 2003. My work with minority students provided me with the tools to accept the new challenge of encouraging students to take more mathematics and to think about adding the math major or math minor to their program of study.

One can see the impact of these efforts across our university. With 600 mathematics majors and 700 mathematics minors, oftentimes the outstanding graduating senior in another department also has a mathematics major or minor. Our mathematics majors who also have another major are being accepted into graduate programs at the most elite universities in their other major.

The work that I do is focused on helping students reach their goals. Given the increasingly important role that mathematics now plays in society, taking more mathematics is essential. Mathematics departments need to communicate this to their students.

### Doctoral Dissertation Defense

James Mixco, Saint Louis University

Thursday, April 11, 10:00am-12:00pm (the first hour is public), in Ritter 202

**Supersymmetric Cluster Algebras and Their Quantum Deformations**

Abstract: Fomin and Zelevinsky introduced cluster algebras in 2001. A cluster algebra is a commutative ring generated by variables obtained by an iterative combinatorial process called mutation. From the time of their inception, cluster algebras have been found to have applications to several branches of mathematics and physics. These include algebraic geometry, Poisson geometry, Teichmuller space theory, combinatorics, and analysis.

More recently, an approach towards defining cluster algebras with Grassmann variables has been proposed by Ovsienko. This attempt has quite a few limitations. Here, we give an approach to supersymmetric cluster algebras independent of Ovsienko and provide some new interesting geometric examples. This work is largely based on the work done by Li, Mixco, Ransingh, and Srivastava. In addition to what is done by Li, Mixco, Ransingh, and Srivastava, we expand the theory of cluster superalgebras by proving theorems analogous to classical cluster algebra theorems. Beyond that, we extend our notion of cluster superalgebras to quantum cluster algebras.

### Colloquium

Mihai Ciucu, Indiana University

Friday, April 12, at 4:10pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

**The interaction of gaps with the boundary in dimer systems --- a heat flow conjecture**

Abstract: We consider a triangular gap of side two in a 90 degree angle on the triangular lattice with mixed boundary conditions: a constrained, zig-zag boundary along one side, and a free lattice line boundary along the other. We study the interaction of the gap with the corner as the rest of the angle is completely filled with lozenges. We show that the resulting correlation is governed by the product of the distances between the gap and its three images in the sides of the angle. This, together with a few other results we worked out previously, provides evidence for a unified way of understanding the interaction of gaps with the boundary under mixed boundary conditions, which we present as a conjecture. Our conjecture is phrased in terms of the steady state heat flow problem in a uniform block of material in which there are a finite number of heat sources and sinks. This new physical analogy is equivalent in the bulk to the electrostatic analogy we developed in previous work, but arises as the correct one for the correlation with the boundary.

The starting point for our analysis is an exact formula we prove for the number of lozenge tilings of certain trapezoidal regions with mixed boundary conditions, which is equivalent to a new, multi-parameter generalization of a classical plane partition enumeration problem (that of enumerating symmetric, self-complementary plane partitions).

### Colloquium

Louis H Kauffman, University of Illinois Chicago

Friday, March 22, at 4:10pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

**Introduction to Virtual Knot Theory**

Abstract: Virtual knot theory studies the knot theory of embeddings of circles in thickened surfaces. By taking projections of the knot diagrams in surfaces to the plane one obtains a theory of diagrams that contain classical knot crossings and virtual crossings that are neither over nor under. The virtual crossings are an artifact of the projection of the knot to the plane but are very useful for the combinatorial topology. Virtual crossings also occur in planar projections of non-planar graphs, and there are many analogies between graph theory and knot theory in this domain. The talk will discuss invariants of virtual knots such as the Jones polynomial in Kauffman bracket form, the odd writhe, the Manturov Parity Bracket, the Arrow polynomial and the Affine Index Polynomial. This theory has many interesting examples and many relations with classical knot theory

and with combinatorics and graph theory. The talk will be self-contained.

### Statistics Seminar

Timothy Keller, SLU

Tuesday, February 26 at 2:30pm in Ritter 106.

**Sampling, Elephants, Agricultural Estimates, and Survey Non-Response**

A brief discussion of the Horvitz-Thompson Theorem and its relation to survey sampling theory in practice is presented, followed by an application that illustrates the issues of making estimates when one doesn't have the sort of data one would like to have.

The talk should be accessible at the level of an undergraduate who has completed a calculus based introductory statistics course, but will also introduce an applied research topic.

### Colloquium

Tyler Bongers, Washington University in Saint Louis

Friday, March 1 at 4:10pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

**Stretching and rotation properties of quasiconformal maps**

Abstract: Quasiconformal maps in the plane are homeomorphisms that satisfy useful distortion inequalities: they map infinitesimal circles to ellipses. These maps arise naturally in complex dynamics and geometric function theory, as well as the study of elasticity and elliptic PDEs. In this talk, we will consider the local geometric properties of these maps and discuss the construction of extremizers for certain geometric regularity conditions related to stretching and rotation. This work will improve upon recent results of Astala-Iwaniec-Prause-Saksman and Hitruhin.

### Colloquium

Liberty Vittert, Washington University in Saint Louis

Friday, February 15 at 4:10pm in Ritter 202 with refreshments beforehand in the Ritter Hall Lobby.

**How to Empower the Public to Understand Numbers**

Abstract: Trying to explain your work to the general public can vary between glazed eyes and genuine fear of the subject. What the public doesn’t understand is that they themselves use statistics and probability every single day- from deciding whether to take an umbrella or which route to drive to work- every person performs some kind of statistical or risk analysis on any given day.

This is a subconscious computation, but with the amount of information currently being measured, ‘fake news’ being reported, and a general miscommunication (if not deliberate mislead) of the facts, how do we help the public understand the power of statistics?

We simplify the numbers enough to empower individuals to feel that they themselves know what questions they should be asking of the data. Sometimes we have to walk a thin line between being “correct” and understandable. How do we do that?

### Colloquium

Xiang Tang, Washington University in Saint Louis

*Note different day of week!* Tuesday, January 29 at 4:10pm in Ritter 202 with refreshments beforehand in the Ritter Hall Lobby.

**An Analytic Grothendieck Riemann Roch Theorem**

Abstract: In this talk, we will introduce an interesting index problem naturally associated to the Arveson-Douglas conjecture in functional analysis. This index problem is a generalization of the classical Toeplitz index theorem, and connects to many different branches of Mathematics. In particular, it can be viewed as an analytic version of the Grothendieck Riemann Roch theorem. This is joint work with R. Douglas，M. Jabbari, and G. Yu.

### Colloquium

Daniel Spector, National Chiao Tung University in Hsinchu, Taiwan

Friday, January 18 at 4:00pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

**New Directions for Harmonic Analysis on L ^{1}**

Abstract: Classical work in harmonic analysis has led us to a thorough understanding of the right spaces from the standpoint of singular integral operators, in the most basic setting, L^{p} spaces and the Hardy space H^{1}. These spaces, in turn, can be used for estimates of integral operators such as the Newtonian and Riesz potentials. Interestingly, in the endpoint p=1 the Hardy space is not necessary to obtain such an estimate, as one can make a weaker assumption and obtain the same strength of conclusion. In this talk we discuss this phenomena, past and present, and give an idea of what might be in its future.

### Geometry-Topology Seminar

TIME+DATE : 4:10pm--5:00pm Tue 27 Nov 2018

ROOM : 216 Ritter Hall

TITLE: Lie Representation Theory, Frames, and Wavelets, I: Introduction

SPEAKER: Brent Wessel, SLU

ABSTRACT: An important topic when studying Lie groups is the representation theory behind it and how we can relate representations to orbits of certain actions. I will give an overview of the construction and decomposition of wavelet representations of a certain class of nilpotent groups. These will then be used to develop a Calderon condition for the existence of admissible vectors for these groups. The first talk will be focused on some of the background in Lie and representation theory while the second talk will zoom in on a particular class of examples. Graduate students with first-year analysis, topology, and algebra are encouraged to attend, especially the first talk on the background information.

### Math-CS club

TIME+DATE: 4:10-5:00pm Wed 11/28

ROOM : Ritter TBD

Title: Info session on REU in computational arithmetic dynamics

Speaker: Benjamin Hutz, SLU

### Geometry-Topology Seminar

TIME+DATE : 4:10pm--5:00pm Tue 04 Dec 2018

ROOM : 216 Ritter Hall

TITLE: Lie Representation Theory, Frames, and Wavelets, II: Oscillator Groups

SPEAKER: Brent Wessel, SLU

ABSTRACT: An important topic when studying Lie groups is the representation theory behind it and how we can relate representations to orbits of certain actions. I will give an overview of the construction and decomposition of wavelet representations of a certain class of nilpotent groups. These will then be used to develop a Calderon condition for the existence of admissible vectors for these groups. The first talk will be focused on some of the background in Lie and representation theory while the second talk will zoom in on a particular class of examples. Graduate students with first-year analysis, topology, and algebra are encouraged to attend, especially the first talk on the background information.

### Math/CS Club

Integration Bee

Wednesday, November 14 at 4:00pm in the Ritter Hall Lobby.

All undergraduates are invited to compete in the annual Integration Bee. Solve integrals for fabulous prizes!

### Colloquium

Shmuel Weinberger, University of Chicago

Wednesday, November 14 at 3:30pm in Ritter 202 with refreshments beforehand in the Ritter Hall Lobby.*NOTE DIFFERENT TIME AND DAY.*

**Quantitative Topology?**

Abstract: Topology is ordinarily thought of as a qualitative subject - can one map be deformed into another? Are these two spaces homomorphic? However, Rutherford said, "Qualitative is nothing but poor quantitative." I would like to discuss some issues that arise when trying to make topology quantitative.

### SLAMS Inaugural Meeting

Wednesday, November 14 at 6pm. Pere Marquette Gallery, DuBourg Hall, 221 N Grand Blvd on the campus of Saint Louis University.

The Saint Louis Academy of Mathematical Sciences is a gathering of researchers in all areas of the mathematical sciences in the Saint Louis region.

Talk at 6 pm: Efim Zelmanov, UCSD

**Infinite dimensional algebras and superalgebras**

Abstract: We will discuss examples, classification and representations of some infinite dimensional superalgebras that arise in Physics.

7:30 pm dinner, jointly hosted by WUSTL and SLU

Talk open to the public. RSVP required for dinner.

### Geometry-Topology Seminar

TIME+DATE : 4:10pm--5:00pm Tue 06 Nov 2018

ROOM : 216 Ritter Hall

TITLE: Fibrations with Aspherical Fiber, II: Invariants

SPEAKER: Seth Arnold, SLU

ABSTRACT: Given an aspherical CW complex *A*, we determine the homotopy groups of the space of self-homotopy equivalences of *A* using elementary obstruction theory arguments. In order to use obstruction theory, tools are developed to deal with the topologies of function spaces. Using a result of J.P. May that classifies *A*-fibrations up to fiber homotopy equivalence over a connected CW complex, we develop two complete cohomological invariants to distinguish such fibrations.

Graduate students who have taken or plan to take General Topology II (fundamental group and covering spaces) are encouraged to attend. Graduate students are also encouraged to give a later talk about their research or about an interesting fact in geometry or topology.

### Geometry-Topology Seminar

TIME+DATE : 4:10pm--5:00pm Tue 30 Oct 2018

ROOM : 216 Ritter Hall

TITLE: Fibrations with Aspherical Fiber, I: Automorphisms

SPEAKER: Seth Arnold, SLU

ABSTRACT: Given an aspherical CW complex *A*, we determine the homotopy groups of the space of self-homotopy equivalences of *A* using elementary obstruction theory arguments. In order to use obstruction theory, tools are developed to deal with the topologies of function spaces. Using a result of J.P. May that classifies *A*-fibrations up to fiber homotopy equivalence over a connected CW complex, we develop two complete cohomological invariants to distinguish such fibrations.

Graduate students who have taken or plan to take General Topology II (fundamental group and covering spaces) are encouraged to attend. Graduate students are also encouraged to give a later talk about their research or about an interesting fact in geometry or topology.

### Colloquium

Christopher Connell, Indiana University

Friday, November 2 at 4:00pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

**Homological Norms on Nonpositively Curved Manifolds**

Abstract: The Gromov-Thurston norm on the singular homology of a closed manifold provides a topological notion of “volume” for a homology class. On the other hand, every such homology class has a dual cohomology class that can be represented by a unique harmonic differential form (with respect to a Riemannian metric) representing that class via the de Rham isomorphism. Forms come equipped with a natural L^{2} norm, and the harmonic norm is the L^{2} norm of this harmonic form. In joint work with Shi Wang, we relate the Gromov-Thurston norm on homology to the harmonic norm on cohomology with upper and lower bounds that depend (necessarily) on the volume and injectivity radius for nonpositively curved manifolds. This extends work of Brock and Dunfield as well as work of Bergeron, Sengun and Venkatesh. We also will discuss some consequences of this relationship between the norms.

### Geometry-Topology Seminar

TIME+DATE : 4:10pm--5:00pm Tue 16 Oct 2018

ROOM : 216 Ritter Hall

TITLE: **A Proof of Gilman's Conjecture**

SPEAKER: Andrew Eisenberg, SLU

ABSTRACT: This talk will cover new research but should still be accessible to graduate students. I will discuss joint work with Adam Piggott proving Gilman's conjecture: any group presented by a finite, monadic, confluent rewriting system must be a free product of finite groups and free groups.

### Colloquium

Kenneth Jacobs, Northwestern

Friday, October 19 at 4:00pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

**Reduction Modulo Infinity**

Abstract: Reduction modulo a prime number p is a very useful tool in arithmetic geometry, and recently it has been applied to study the dynamics of rational maps with algebraic coefficients. Several authors have presented methods for determining when a given rational map has potential good reduction and / or semistable reduction, both of which describe degeneracy that arises when reducing modulo p. By adapting the method of R. Rumely (UGA), we are able to give new, parallel notions of good reduction / semi-stable reduction for rational maps having arbitrary complex coefficients.

### Geometry-Topology Seminar

TIME+DATE : 4:10pm--5:00pm Tue 09 Oct 2018

ROOM : 216 Ritter Hall

TITLE: **Rewriting Systems and Gilman's Conjecture**

SPEAKER: Andrew Eisenberg, SLU

ABSTRACT: This will be a background talk, introducing basic definitions and properties of rewriting systems. Rewriting systems are a way of presenting groups with an eye towards answering algebraic and geometric questions algorithmically. A fundamental goal is to understand how features of groups are encoded by different types of rewriting systems. I'll discuss a collection of related results over the past 40 years and introduce Gilman's conjecture on finite, monadic, confluent rewriting systems.

### Colloquium

Elodie Pozzi, Saint Louis U.

Friday, October 5 at 4:00pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

**A 2D inverse problem in magnetism**

Abstract: Inverse problems have known a recent development in many fields like signal processing, medical imaging and more recently paleomagnetism. Broadly speaking, an inverse problem consists in reconstructing from a set of measurements the original source. We consider a 2D inverse problem in magnetism to estimate the net moment represented by the mean value of a function supported on an interval K of the real line from the partial knowledge of the magnetism on an another interval S located on the parallel line to K at height h>0. We will see how this question can be rephrased using complex analysis, harmonic analysis and operator theory. To estimate the mean value, we will construct and solve a constrained approximation problem. This talk is based on a joint work with Juliette Leblond, INRIA, France.

### Geometry-Topology Seminar

TIME+DATE : 4:10pm--5:00pm Tue 02 Oct 2018

ROOM : 216 Ritter Hall

TITLE: **Compact Hausdorff groups are pro-Lie, II: the proof**

SPEAKER: Qayum Khan, SLU

ABSTRACT: This is a learning talk, continuing the definitions / statements / discussions of Tue 25 Sep 2018. We go through the Pontrjagin--Weil proof of von Neumann's 1933 theorem, that any compact Hausdorff group is the projective limit of Lie groups, using the Peter--Weyl theorem from classical harmonic analysis.

Graduate students who have taken or are taking General Topology I (point-set topology) are encouraged to attend. Graduate students are also encouraged to give a later talk about their research or about an interesting fact in geometry or topology.

### Algebra Seminar

Katie Radler, SLU graduate student

Thursday, September 27 from 10:00am-11:00am in Ritter 106

**On Prufer-like Properties of Leavitt Path Algebras**

Abstract: In this talk we show two characterizing properties of a Prufer domain that hold in a Leavitt path algebra and we show that the cancellation property does not hold in general with a counterexample. We end with necessary and sufficient conditions on a graph so that the Leavitt path algebra of the graph satisfies the cancellation property.

### Statistics Seminar

Tim Keller, Saint Louis U.

Thursday, September 27 from 3:00-4:00pm in Ritter 204

**Stratified Simple Random Sampling with Multiple Estimation Objectives**

Abstract: Non-response is the greatest challenge facing establishment surveys. A major contributing factor for survey non-response is respondent burden. To meet this challenge survey establishments must therefore strive to meet estimation goals with the smallest possible sample size.

A common and basic survey design is the stratified simple random sample, and a common estimate of interest is the population total for a survey item. For this special case, the problem of meeting multiple estimation objectives is formulated as a convex optimization problem, and a numerical method for determining the optimal allocation of a fixed overall sample size is presented.

### Colloquium

Keri Kornelson, Oklahoma.

Friday, September 21 at 4:00pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.

**Norm retrieval via spatiotemporal samples**

Abstract: There is a relaxation of the problem of phase retrieval in which the magnitude of a signal is computed from phaseless measurements. We require less information, so can be possible with fewer measurements than phase retrieval. As a ready example, an orthonormal basis yields norm retrieval measurements. In this talk, we introduce the concepts and earlier results about performing phase and norm retrieval in real, finite-dimensional space. We then present recent work with Fatma Bozkurt in which we do norm retrieval with dynamical samples, i.e. samples obtained at selected measurement points but repeated over time.

### Geometry-Topology Seminar

Qayum Khan, Saint Louis U.

Tuesday, September 25, 4:10pm-5:00pm in Ritter Hall 216

**Compact Hausdorff groups are pro–Lie**

Abstract: This is a learning talk. We go through the Pontrjagin–Weil proof of von Neumann's 1933 theorem, that any compact Hausdorff group is the projective limit of Lie groups, using the Peter–Weyl theorem from classical harmonic analysis. Graduate students who have taken or are taking General Topology I (point-set topology) are encouraged to attend. Graduate students are also encouraged to give a later talk about their research or about an interesting fact in geometry or topology.

### Colloquium

- Friday, September 7 at 4:00pm in Ritter 231 with refreshments beforehand in the Ritter Hall Lobby.
- Haiyan Cai, UMSL.
- Classification and Hypothesis Testing
- Abstract: Robust classification algorithms (random forests, support vector machines, deep neural networks, for example) have been developed in recent years with great success. To take advantage of this development , we recast the classical two-sample test problem in the framework of a classification problem. Based on the estimates of class probabilities from a classifier trained from the samples, we propose a new method for the two-sample test. We explain why such a test can be a powerful test and compare its performance in terms of power and efficiency with those of some other recently proposed tests with some simulation and real-life data. Our method is nonparametric and can be applied to complex and high dimensional data whenever there is a good classifier that provides uniformly consistent estimate of class probabilities for such data. The talk will start with a general introduction of the classification problem in machine learning and the basic concepts in hypothesis testing in statistics.

### Geometry-Topology Seminar

- TIME+DATE : 4:10pm--5:00pm Tue 04 Sep 2018
- ROOM : 216 Ritter Hall
- TITLE: Metric spaces are paracompact
- SPEAKER: Qayum Khan, SLU
- ABSTRACT: This is a learning talk. We go through Mary Ellen Rudin's clever one-page proof of Stone's theorem, which states that all metric spaces are paracompact. We will review all necessary definitions. Graduate students who have taken or are taking General Topology I (point-set topology) are encouraged to attend.