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Events for the weeks of February 8th – 20th

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Tue, Feb. 10 1:25pm (online)	Algebra/Logic Claudia Muresan (University of Bucharest) View Online:https://cuboulder.zoom.us/j/96896272260 Abstracting congruence extensions through complete join–semilattice morphisms between commutator lattices
Tue, Feb. 10 5pm (Math 350)	Math Club Nat Thiem X Come hear about the math department's summer REU program! REU stands for Research Experiences for Undergrads. Our summer REU program is an opportunity for you to gain experience and see what math research is like. Once available, descriptions of the different projects will be posted at www.colorado.edu/math/undergraduate-program/summer-research-undergraduate. Or come to the info session to hear about the projects and get your questions answered! Summer REU Info Session
Wed, Feb. 11 2:10pm (Math350)	Math Phys Gregory Berkolaiko (Texas A&M University) View Online:https://cuboulder.zoom.us/j/97049173677 X As a warm-up for the semester, we will explore the time evolution in a finite-dimensional (d=2 mostly) Schrödinger equation, its relation to the quadratic form and their visualization on the Bloch sphere. If time permits, we will briefly discuss why a 2-dimensional picture is sometimes appropriate even when working with unbounded Schrödinger operators. Warm-up: Visualizing Schrödinger's equation in finite dimensions
Wed, Feb. 11 4:40pm (MATH 3…	Grad Student Seminar Colin Jackson X What makes a function earn the title of a zeta function? We will start by looking at the Riemann zeta function, and then generalizations of it and see that if it walks like a zeta function and quacks like a zeta function, then its a zeta function Zeta Function 101
Thu, Feb. 12 11:15am (MATH …	Algebraic Geometry Bob Kuo X In this talk, we'll discuss tropical and toric geometry, and a relationship between the two given by Mustafin varieties. A degenerate analogue to projective geometry part II
Thu, Feb. 12 2:30pm (MATH 3…	Functional Analysis Robin Deeley (CU Boulder) X I will introduce a class of dynamical systems called shifts of finite type. There are a number of C-algebras one can construct from a shift of finite type. I will discuss properties of these C-algebras such as rational Poincare duality and rational isomorphism. Rationalizing shifts of finite type
Fri, Feb. 13 12:20pm (MATH …	Math Edu Shelby Stanhope (US Air Force Academy) View Online:https://cuboulder.zoom.us/j/99367133807 X Students often find the transition from two-dimensional to three-dimensional thinking in multivariable calculus challenging. Computer visualization and tactile models can help bridge this gap and deepen students’ spatial understanding of concepts. CalcPlot3D is a free, web-based applet for 3D graphing that is easy for students and instructors to use due to its code-free, menu-driven interface with fillable textboxes, dropdown lists, and checkboxes. In this presentation, I will show demonstrations that instructors can use to illuminate concepts and visualizations that students can easily create themselves. In addition, I will discuss several classroom activities that incorporate 3D-printed models, allowing students to physically explore concepts in small groups. Together, these tools provide engaging ways for instructors to support student learning and help cultivate stronger geometric intuition in multivariable calculus. Supporting conceptual understanding in multivariable calculus using computer visualization and classroom activities with 3D-printed models
Tue, Feb. 17 2:30pm (MATH 3…	Lie Theory Carlos Ortiz (Colorado State University) X A fundamental problem in topology is to determine when two spaces are distinct. For surfaces, classical invariants suffice, but for three-dimensional manifolds the question is considerably harder. The Witten-Reshetikhin-Turaev invariants, originating in quantum field theory, provide one family of tools. For torus bundles, i.e. 3-manifolds built by cutting a torus, applying a mapping class in SL(2,Z), and regluing, the skein algebra embeds into a non-commutative torus at roots of unity, yielding a finite-dimensional representation that makes these invariants concretely computable. Exploiting this structure, we develop a classical dynamic programming algorithm and a quantum algorithm that encodes the computation into logarithmically many qubits, achieving an exponential reduction in space. We further identify a natural coefficient-counting problem that is #P-complete yet admits efficient quantum approximation. The first half of the talk will be expository, requiring only linear algebra and modular arithmetic. The second half will outline the algorithmic results. How to tell shapes apart using quantum computers
Tue, Feb. 17 3:30pm (MATH 3…	Topology Gregory Berkolaiko (Texas A&M) X The Rayleigh-Ritz method approximates the eigenvalues of a large Hermitian matrix B with Ritz values, which are the eigenvalues of B's restriction() to a smaller trial subspace S. We can view the k-th Ritz value as a real-valued function ("Ritz energy landscape") on the manifold of all possible s-dimensional trial subspaces, the Grassmannian (or for the real symmetric case). Motivated by questions from quantum chemistry and spectral optimization, this talk explores the topology of the Ritz energy landscape. A Morse function is called "perfect" if it describes the topology of its domain in the most efficient way possible, meaning the number of its critical points of each type exactly matches the corresponding Betti number of the space. We demonstrate that for a matrix B with distinct eigenvalues, the Ritz landscape is indeed perfect. While the function itself is not everywhere smooth and its critical points are not isolated --- and not even Morse-Bott --- its critical structure is nevertheless well-defined and ultimately reflects the topology of the Grassmannian in a minimal, perfect way. To be more precise, we show that the filtration of the Grassmannian by the sublevel sets of the k-th Ritz value is homologically perfect. The proof proceeds by introducing a suitable perturbation which ensures that points of non-smoothness are not critical (by a theorem of Zelenko and the presenter) and that the remaining smooth critical points are isolated. Based on a joint work with Mark Goresky (IAS). Footnote (): the term "restriction" is appropriate in the equivalent formulation of eigenvalues of quadratic forms. For an operator B, we apply it to vectors in S and then project the result orthogonally back onto S; this is called a "compression" of B. Ritz energy landscape is perfect (almost) Morse
Tue, Feb. 17 5pm (Math 350)	Math Club Edouard Heitzmann X The legal standard set in Rucho v Common Cause puts the onus on the plaintiffs in a Voting Rights Act (VRA) case to demonstrate that a map is a racial rather than a partisan gerrymander in order for it to be struck down as unlawful. This means plaintiffs have to 'do the homework' of the defendants for them: they must produce a map that is at least as politically gerrymandered as the defendants drew, while achieving better racial representation outcomes. This standard was successfully met by a group of mathematicians in the El Paso redistricting case, winning in federal court before the Supreme Court shadow docket put a hold on the decision, allowing the racial gerrymander to go through. The mathematicians who accomplished this used Monte Carlo Markov Chain (MCMC) methods to draw a so-called 'ensemble' of millions of alternative congressional maps for Texas, and used statistical methods to show that the enacted map was an outlier for racial representation among the maps that had similar partisan outcomes. In this talk I will go over these mathematical details, as well as describe the computational tools currently used in this field. Note: If you have a working Jupyter Notebook installation, you are encouraged to bring it to the talk, as you will have the opportunity to follow along the computational demos included in the talk. The Mathematics of Redistricting—what they did in Texas

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