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Tue, 22. Apr at 11:15
1.023 (BMS Room, ...
W-constraints for the ancestor potential of (r,s)-theta classes
Abstract. Witten’s conjecture, which was proved by Kontsevich, states that the generating series for intersection numbers on the moduli space of curves is a tau-function for the KdV integrable hierarchy. It can be reformulated as the statement that the ancestor potential of the trivial cohomological field theory is the unique solution to a system of differential constraints that form a representation of the Virasoro algebra. In this talk I will present a new generalization of this celebrated result. The object of study becomes the ancestor potential of an interesting set of cohomology classes on the moduli space of curves, called (r,s) theta classes, which form a non-semisimple cohomological field theory. (Here, r is a positive integer and s is a positive integer between 1 and r-1.) The (r,s) theta classes are constructed as the top Chern classes of the Chiodo classes, and can be understood as a higher generalization of the Norbury classes. We show that the ancestor potential is the solution of a system of differential constraints that form a representation of a W-algebra. However, the differential constraints form an Airy structure (and thus uniquely fix the ancestor potential) only in the cases s=1 and s=r-1. An equivalent way of stating this result is that we determine loop equations satisfied by the correlators for all (r,s), but only when s=1 or s=r-1 are the loop equations uniquely solved by (shifted) topological recursion. This talk is based on work in progress with N. K. Chidambaram, A. Giacchetto and S. Shadrin and previous work by many people such as https://arxiv.org/abs/2412.09120, https://arxiv.org/abs/2408.02608, https://arxiv.org/abs/2205.15621, https://arxiv.org/abs/1812.08738, to name a few.
Tue, 22. Apr at 13:00
2.417
A novel multipoint stress control volume method for linear elasticity on quadrilateral grids
Wed, 23. Apr at 11:30
online
Entanglement Detection via Frank-Wolfe Algorithms
Abstract
Wed, 23. Apr at 13:00
ZIB, Room 2006 (S...
Multi-node quantum circuit simulation with decision diagram in HPC
Abstract. Decision diagram is a data structure that has been used for a long time to represent logic functions. Recently, the development of quantum computers has become very active, and decision diagrams are used in quantum circuit simulation because it can represent quantum states (complex vectors) and quantum gates (complex unitary matrices) with less memory. In this presentation, I will explain a method for large-scale parallelization of quantum circuit simulations using decision diagrams in an HPC (High-Performance Computing) environment. I will also discuss the difference between quantum circuits that can be simulated quickly with decision diagrams and those that are slow, and discuss suitable applications.
Wed, 23. Apr at 15:15
rooms 405/406
On stochastic homogenisation of integral functionals and differential operators
Abstract
Wed, 23. Apr at 16:00
Wed, 23. Apr at 16:15
Arnimallee 3
Extra-tight Euler trails in hypergraphs
Abstract. An extra-tight trail in a hypergraph is like a normal tight trail in a hypergraph, but where you also consider the edges that "skip" exactly one vertex of the trail. We will consider the question which hypergraphs contain extra-tight Euler trails. We will show that large graphs with high minimum degree always have an extra-tight Euler trail if certain "trivial" degree divisibility constraints are satisfied. The proof uses the technique of absorption. Joint work with Stefan Glock, Olaf Parczyk, and Tibor SzabĂł
Wed, 23. Apr at 16:30
EN 058
Colored multiset Eulerian polynomials
Abstract. The central objects in this talk are the descent polynomials of colored permutations on multisets, referred to as colored multiset Eulerian polynomials. These polynomials generalize the colored Eulerian polynomials that appear frequently in algebraic combinatorics and are known to admit desirable distributional properties, including real-rootedness, log-concavity, unimodality and the alternatingly increasing property. In joint work with Bin Han and Liam Solus, symmetric colored multiset Eulerian polynomials are identified and used to prove sufficient conditions for a colored multiset Eulerian polynomial to satisfy the self-interlacing property. This property implies that the polynomial obtains all of the aforementioned distributional properties as well as others, including bi-gamma-positivity. To derive these results, multivariate generalizations of a generating function identity due to MacMahon are deduced. The results are applied to a pair of questions, both previously studied in several special cases, that are seen to admit more general answers when framed in the context of colored multiset Eulerian polynomials. The first question pertains to s-Eulerian polynomials, and the second to interpretations of gamma-coefficients. We will see some of these results in detail, depending on the pace of the talk. We may also discuss some connections between multiset permutations and polytopes from algebraic statistics.
Thu, 24. Apr at 13:30
Faster computations of Ehrhart, statistics of zonotopes in Sagemath
Thu, 24. Apr at 15:15
Rudower Chaussee ...
Solving Nonlinear Problems to Global Optimality
Abstract. In this talk, we provide an overview of Gurobi's algorithmic components for solving nonlinear optimization problems to global optimality. In essence, we extend our existing mixed-integer programming (MIP) framework to handle such problems. This includes our presolve algorithms, an extension of the branch-and-bound method utilizing spatial relaxations, and an interior point algorithm for nonlinear problems, which serves as a primal heuristic to find high-quality solutions. As a result, we can compute solutions to nonlinear optimization problems along with certificates for global optimality. Finally, we have extended gurobipy to facilitate the easy formulation of expression-based nonlinear optimization problems in Python. Gurobi's nonlinear solver applies to explicit expression-based constraints and does not require the supply of derivative data.
Fri, 25. Apr at 13:00
TU Berlin, StraĂźe...
What is What is...the calculus of variations?
Abstract. This talk offers a brief introduction to the calculus of variations, focusing on the core ideas behind variational problems and their role in describing systems governed by energy principles. We will explore how such methods arise in the modeling of grain boundaries in polycrystalline materials. The talk also includes a short overview of the concept of Γ-convergence, an important tool for studying the asymptotic behavior of variational problems.
Fri, 25. Apr at 14:15
TU (C 130)
Emergence of defects at grain boundaries: Variational analysis (Kovalevskaya Lecture)
Tue, 29. Apr at 11:15
1.023 (BMS Room, ...
Verlinde's formula in logarithmic conformal field theory
Abstract. Verlinde's formula for rational two-dimensional conformal field theory says that the fusion rules can be computed from the modular transformations of characters. Thanks to Yi-Zhi Huang this is a theorem for rational vertex operator algebras. I will give a historical introduction to the subject and then introduce a setting in which this statement also holds for logarithmic conformal field theories.
Tue, 29. Apr at 13:00
2.417
Wed, 30. Apr at 10:00
HVP 11 a, R.313
Wed, 30. Apr at 13:00
2.417
Wed, 30. Apr at 15:15
Library, room 411
Nonlocal analysis of energies in micromagnetics
Abstract
Wed, 30. Apr at 15:45
Rudower Chaussee ...
Wed, 30. Apr at 16:30
EN 058
Wed, 30. Apr at 18:00
FU Berlin,  Insti...
 Was sind Zahlen? Intuition oder Axiomatik in der Mathematik
Abstract.  Obwohl die Zahlen seit Jahrtausenden nicht nur von Mathematikern richtig verwendet werden, wurden sie erst vor 150 Jahren axiomatisch begründet. Warum hat das so lange gedauert? Weil die Zahlen zwar intuitiv richtig verwendet werden, man aber nicht wusste (und eigentlich noch immer nicht weiß), warum. Warum ist es sinnvoll, die Summe 20 + 30 zu bilden, wenn diese Zahlen Anzahlen von Personen beschreiben, aber nicht, wenn es sich um Temperaturen handelt? Liegt die Anwendung der Zahlen (und überhaupt mathematischer Objekte) außerhalb der Mathematik? Will man Zahlen anwenden, muss man die bei der Axiomatisierung vorgenommene Identifizierung von Ordinal- und Kardinalzahlen rückgängig machen. Das teilt einige Objekte der angewandten Mathematik in zwei duale Welten. In der einen finden sich Ordinalzahlen, intensive physikalische Größen und stetige Funktionen wieder. In der anderen liegen Kardinalzahlen, extensive physikalische Größen und Radonmaße. Die Verwechslung dieser beiden Welten sollte vermieden werden, wenn man möchte, dass entwickelte mathematische Modelle die physische Realität möglichst gut widerspiegeln.
Wed, 07. May at 11:30
online
A New Approach to Metastability in Multi-Agent Systems
Abstract
Wed, 07. May at 13:15
Room: 3.007 John ...
Wed, 07. May at 15:15
rooms 405/406, WI...
On a generalization of the Bardos-Tartar conjecture to nonlinear dissipative PDEs
Abstract
Wed, 07. May at 15:15
WIAS, Erhard-Schm...
Wed, 07. May at 16:00
Wed, 07. May at 16:00
Mon, 12. May at 14:00
1.023 (BMS Room, ...
Symplectic groupoid and cluster algebras
Abstract. The symplectic groupoid is a set of pairs (B,A) with A unipotent upper-triangular matrices and B in GLn being such that the matrix A~ = BABT is itself unipotent upper triangular. It turned out recently that the problem of description of such pairs can be explicitly solved in terms of Fock--Goncharov--Shen cluster variables; moreover, for B satisfying the standard semiclassical Lie--Poisson algebra, the matrices B, A, and A~ satisfy the closed Poisson algebra relations expressible in the r-matrix form. Since works of J.Nelson, T.Regge and B.Dubrovin, it was known that entries of A can be identified with geodesic functions on Riemann surfaces with holes. In our approach, we are able to construct a complete set of geodesic functions for a closed Riemann surface. We have a complete description for genus two; I'm also about to discuss moduli spaces of higher genera. Based on my joint papers with MIsha Shapiro and our students.
Tue, 13. May at 13:00
2.417
Wed, 14. May at 10:00
HVP 11 a, R.313
Estimation and classification for DNN: Bless of dimension
Wed, 14. May at 13:15
Room: 3.007 John ...
Wed, 14. May at 14:00
rooms 405/406
Solvability and optimal control in spatially structured epidemic models
Abstract
Wed, 14. May at 15:30
rooms 405/406
Mathematical models of active phase separation and droplet dynamics
Abstract
Thu, 15. May at 16:15
TU Berlin, Instit...
Thu, 15. May at 17:15
TU Berlin, Instit...
Fri, 16. May at 09:00
1.023 (BMS Room, ...
Moduli spaces of curves and the classification of integrable systems
Abstract. I will present several results and conjectures on the classification of different classes of integrable systems of evolutionary PDEs, up to the appropriate transformation groups. These include Hamiltonian systems, tau symmetric systems and systems of conservation laws. I will then explain in what sense we expect that integrable systems arising from intersection theory on the moduli space of stable curves are universal objects with respect to these classifications. In the rank one case I will present strong evidence in support of these claims. This is joint work with A. Buryak.
Fri, 16. May at 10:00
1.023 (BMS Room, ...
On the DR/DZ equivalence
Abstract. There are two main recipes to associate to a Cohomological Field Theory (CohFT) an integrable hierarchy of hamiltonian PDEs: the first one was introduced by Dubrovin and Zhang (DZ, 2001), the second by Buryak (DR, 2015). It is interesting to notice that the latter relies on the geometric properties of the Double Ramification cycle — hence the name DR — to work. As soon as the second recipe was introduced, it was conjectured that the two had to be equivalent in some sense, and it was checked in a few examples. In the forthcoming years several papers by Buryak, Dubrovin, Guerè, Rossi and others followed, checking more examples of CohFTs, making the conjecture more precise, proving the conjecture in low genera, and eventually turning the statement of the conjecture in a purely intersection theoretic statement on the moduli spaces of stable curves. Lately, the conjecture was proved in its intersection theoretic form, employing virtual localisation techniques. (j.w.w. Blot, Rossi, Shadrin).
Fri, 16. May at 11:30
1.023 (BMS Room, ...
Leaky Hurwitz numbers and topological recursion
Abstract. Leaky Hurwitz numbers were introduced by Cavalieri-Markwig-Ranganathan by extending the branching morphism from the logarithmic double ramification cycle to its pluricanonical counterpart. These numbers also have a natural interpretation in terms of tropical geometry and yield (non-hypergeometric) KP tau functions. I will explain how to think about these numbers, and how we can extend the recent works of Alexandrov-Bychkov-Dunin-Barkowski-Kazarian-Shadrin to prove (at least blobbed) topological recursion. Along the way, I will interpret the cut-and-join operator as a hamiltonian whose flow generates the spectral curve. This is joint work in progress with M. A. Hahn.
Wed, 21. May at 11:30
online
Demand Strip Packing
Wed, 21. May at 15:15
WIAS, Erhard-Schm...
Uncertainty quantification for a model for a magnetostrictive material involving a hysteresis operator
Wed, 21. May at 16:00
Wed, 21. May at 16:00
Thu, 22. May at 17:15
TU Berlin, Instit...
Fri, 23. May at 14:15
TU (C 130)
Wed, 28. May at 15:15
WIAS, Erhard-Schm...
Wed, 28. May at 16:30
Rudower Chaussee ...
A lower bound on the normal radius of hypersurfaces with applications to bounded geometries with boundary
Abstract
Wed, 04. Jun at 11:30
online
On the Expressivity of Neural Networks
Abstract
Wed, 04. Jun at 15:15
WIAS, Erhard-Schm...
Thu, 05. Jun at 16:15
TU Berlin, Instit...
Wed, 11. Jun at 15:15
WIAS, Erhard-Schm...
Wed, 11. Jun at 16:30
EN 058
Entropy profiles and algebraic matroids
Abstract. Consider the uniform probability distribution on the solution set of a polynomial system with coefficients in a finite field k. When K ranges over the finite extensions of k, this defines a sequence of distributions and we are interested in their Shannon entropy profiles. Using results from the model theory of finite fields, we identify all convergent subsequences and compute their limits. The computability part relies on a difficult symbolic algorithm known as Galois stratification. In the special case that the polynomials define a k-irreducible algebraic variety, one of these limits turns out to be its algebraic matroid, which recovers a result previously obtained by F. Matúš.
Wed, 18. Jun at 11:30
online
Convolutional Brenier Generative Networks
Abstract
Wed, 18. Jun at 13:00
ZIB, Room 2006 (S...
Bounding geometric penalties in Riemannian optimization
Abstract. Riemannian optimization refers to the optimization of functions defined over Riemannian manifolds. Such problems arise when the constraints of Euclidean optimization problems can be viewed as Riemannian manifolds, such as the symmetric positive-definite cone, the sphere, or the set of orthogonal linear layers for a neural network. This Riemannian formulation enables us to leverage the geometric structure of such problems by viewing them as unconstrained problems on a manifold. The convergence rates of Riemannian optimization algorithms often rely on geometric quantities depending on the sectional curvature and the distance between iterates and an optimizer. Numerous previous works bound the latter only by assumption, resulting in incomplete analysis and unquantified rates. In this talk, I will discuss how to remove this limitation for multiple algorithms and as a result quantify their rates of convergence.
Wed, 18. Jun at 16:00
Wed, 18. Jun at 16:00
Thu, 19. Jun at 15:15
Rudower Chaussee ...
Wed, 25. Jun at 13:15
Room: 3.007 John ...
Wed, 25. Jun at 15:15
WIAS, Erhard-Schm...
Fri, 27. Jun at 14:15
Urania
Wed, 02. Jul at 11:30
online
Informing Opinion Dynamics Models with Online Social Network Data
Abstract
Wed, 02. Jul at 15:15
WIAS, Erhard-Schm...
Wed, 02. Jul at 16:00
Wed, 02. Jul at 16:00
Thu, 03. Jul at 15:15
Rudower Chaussee ...
Thu, 03. Jul at 16:15
TU Berlin, Instit...
Thu, 03. Jul at 16:15
TU Berlin, Instit...
Fri, 04. Jul at 14:15
TU (C 130)
Kovalevskaya Lecture
Sun, 06. Jul at 15:30
Rudower Chaussee ...
Positive sectional curvature and Ricci flow
Abstract
Wed, 09. Jul at 15:15
WIAS, Erhard-Schm...
The three limits of the hydrostatic approximation
Abstract
Wed, 16. Jul at 11:30
online
Data-Adaptive Discretization of Inverse Problems
Abstract
Wed, 16. Jul at 15:15
WIAS, Erhard-Schm...