**Hosts:**

Herbert Edelsbrunner, Matthew Kwan and Uli Wagner

**Coordinates:**

Default time: Wednesday, at 13:00

Default place: Mondi 3 seminar room, Central Building, Am Campus 1, 3400 Klosterneuburg, Austria

Please contact Vojtěch Kaluža if you want to be notified about upcoming talks, if you want to give one or if you want access to recordings of previous talks (if available and assuming the speaker gave permission).

**Upcoming talks:**

**Date:** 29th of November**Speaker:** Márton Naszódi (Rényi Institute, Budapest)

**Title:**Quantitative Helly and Steinitz type theorems

**Abstract:**According to Helly’s theorem, if the intersection of any d+1 members of a finite family of convex sets in R^d is not empty, then the sets contain a point in common. In a similar vein, a classical result of Steinitz states that if the origin belongs to the interior of the convex hull of a set S in R, then there are 2d points of S whose convex hull contains the origin in the interior. Bárány, Katchalski and Pach considered quantitative versions of both results, that is when ‘not empty’ is replaced by some measure of size, say ‘of volume at least one’, and similarly, ‘a point in the interior’ is replaced by the containment of a ball of certain radius. We will survey some of the recent advances in the area and point to some open problems. A large part of the results is joint work with Grigory Ivanov.

**Past talks:**

date | speaker | title |
---|---|---|

23rd of November | Imre Bárány (Rényi Institute, Budapest) | Pairwise intersecting convex sets and cylinders in R^3 |

22nd of November | Lucy Tobin (U Sydney) | Many-Vertex Triangulations of 4-Manifolds |

8th of November | Yuval Wigderson (ETH Zürich) | Ramsey properties of random graphs |

25th of October | Alex Bronstein (Technion and ISTA) | Spectral approaches to deformable shape analysis |

27th of September | Manuel Soriano Trigueros (ISTA) | Block functions and induced matchings: new invariants for morphisms of persistence modules. |

16th of August | Alp Müyesser (UCL) | Optimal spread for spanning subgraphs |

12th of July | Alexey Garber (UTRGV) | Weighted Ehrhart Theory: Extending Stanley's Nonnegativity Theorem |

31st of May | Christian Krattenthaler (Uni Wien) | Growth diagrams and crossings and nestings in matchings and set partitions |

26th of April | Benedikt Stufler (TU Wien) | Limits of random cubic planar graphs |

12th of April | Oswin Aichholzer (TU Graz) | Combinatorial reconfiguration in plane graphs - A short overview and open problems |

22nd of March | Michael Drmota (TU Wien) | Pattern Occurrence Counts in Random Planar Maps |

8th of March | János Pach (Rényi Institute and ISTA) | Two geometric applications of the linear algebra method |

22nd of February | Amit Patel (Colorado State University) | The Persistence Diagram as a Möbius Inversion |

8th of February | Mohammad Farshi (Yazd University) | Some Results on (Weakly) Self-approaching, Increasing-Chord, and Angle-Monotone Geometric Networks |

25th of January 2023 | Patrick Schnider (ETH Zurich) | Combinatorial Depth Measures and the Cascade Conjecture |

18th of January 2023 | Martin Bauer (Florida State University) | Shape Analysis: the challenge of geometric data |

7th of December | Michael Anastos (ISTA) | Longest Cycles in Sparse Random Graphs and Where to Find Them |

5th of October | Günter Rote (FU Berlin, ISTA) | Grid Peeling and the Affine Curve-Shortening Flow |

21st of September | Adam Brown and Ondřej Draganov (both ISTA) | Computational derived sheaf theory |

14th of September | Mehtaab Sawhney (MIT) | Online Edge Coloring via Tree Recurrences and Correlation Decay |

7th of September | Zachary Hunter (Oxford University) | Some bounds on the van der Waerden numbers |

3rd of August | Roy Meshulam (Technion) | Complexes of injective words |

13th of July | Boris Aronov (New York University and ISTA) | Polynomial partitioning: an introduction and a sloppy review, with applications |

6th of July | Oliver Cooley (ISTA) | Generalisations of connectedness in random graphs |

22nd of June | Kristóf Huszár (Inria Sophia Antipolis - Méditerranée) | On The Width of Complicated JSJ Decompositions |

15th of June | Matthew Kwan (ISTA) | High–girth Steiner triple systems |

1st of June 2022 | Jacob Steinberg (Woods Hole Oceanographic Institute) | Ocean Energetics: from varied observations of mesoscale turbulence to sea level change in response to warming |

25th of May 2022 | Abigail Thompson (UC Davis) | Constructing trisections of 4-manifolds |

11th of May 2022 | Joel Hass (UC Davis) | The space of shapes and applications to biology |

4th of May 2022 | János Pach (Rényi Institute & ISTA) | What is geometric graph theory? |

3rd of December 2021 | Vladimir Kolmogorov | Generalized minimum 0-extension problem and discrete convexity |

25th of November 2021 | Frank Nielsen, Sony Computer Science Laboratories Inc. (Sony CSL) | Bregman divergences, dual information geometry, and generalized convexity |

14th of October 2021 | Martin Tancer (Charles University) | Parametrized complexity of untangling knots |

29th of September 2021 | Denys Bulavka (Charles university) | Weak saturation of multipartite hypergraphs |

1st of September 2021 | Jakub Opršal | Homotopy in complexity classification of promise graph colouring |

July 7th at 13:00 | Natan Rubin | Stronger bounds for Weak Epsilon-Nets in Higher Dimensions |

June 30th at 14:00 | Adam Brown | Topological Structure of Ocean Eddies |

June 23rd 2021 | Sergey Avvakumov (Copenhagen) | A subexponential size triangulation of ${\mathbb R}P^n$. |

June 16th 2021 at 13:00 | Eddie Aamari (LPSM, Paris) | Statistical Query Complexity of Manifold Estimation |

19th of May 2021 at 13:00 | Álvaro Torras Casas (Cardiff) | Persistence Mayer-Vietoris Spectral Sequences by example |

5th and 12th of May 2021 | Mathijs Wintraecken | Tracing Isomanifolds in $\mathbb{R}^{d}$ in Time Polynomial in d using Coxeter-Freudenthal-Kuhn Triangulations. |

21st of April 2021 | Michael Baake (Bielefeld) | Aperiodic Order - Tilings, Projection Method, Spectra: Part II |

14th of April2021 | Uwe Grimm (open University UK) | Aperiodic Order - Tilings, Projection Method, Spectra: Part I |

31st of March 2021 | Dominique Attali (Gipsa-lab Grenoble) | Reconstructing manifolds by weighted $\ell_1$-norm minimization |

24th of March 2021 | Alexey Garber (Texas and a long term visitor of the Edelsbrunner group) | Regularity radius for Delone sets |

24th of February continued on the 3rd of March 2021 | Alexey Garber (Texas and long term visitor) | Convex polytopes that tile space with translations: lattices and Voronoi domains. |

February 10th, 2021, 13:00 (Vienna time), on Zoom. | Nicolò Zava (University of Udine) | Quasi-metric: a distance notion in non-symmetric environments |

January 27th, 2021, 16:00 (Vienna time) | Pablo Soberón (Baruch College, City University of New York) | The topological Tverberg theorem beyond prime powers |

13th of January 2021, 16:00 Vienna time | Erin Chambers (St. Louis) | Quantifying Shape Using the Medial Axis |

December 16, 2020 | Alexey Balitskiy (MIT) | Urysohn width bounds |

October 28, 2020 | Günter Rote (FU Berlin) | Random polytopes and the wet part for arbitrary probability distributions |

11th October 2020 | Hana Kourimska | Discussion session |

October 21, 2020 | George Francis (Illinois) | Interactive Animations of Classical Homotopies |

Wednesday, June 17, 2020 | Ziga Virk | Detecting geodesic circles with persistent homology |

June 10 and 17, 2020 | Hana Kourimska | Discrete Riemann surfaces and beyond |

April 1, 2020 | Mathijs Wintraecken | Topological integral invariants |

Thursday, March 5, 2020 | Emo Welzl | Sylvester's Four-Point Problem on Order Types |

Wednesday, March 4, 2020 | Amir Jafari | Chromatic number of Kneser hypergraphs and a conjecture of Frick |

Wednesday, February 12, 2020 | Farid KARIMIPOUR | Topological Data Analyis for Geospatial Data |

11th of February, 2020 14:00 | André Lieutier | Lexicographic optimal chains and manifoldtriangulations |

Wednesday, February 5, 2020 | Grisha Ivanov | No-dimension versions of Caratheodory's and Tverberg's theorems in Banach spaces and their corollaries. |

Wednesday, January 22, 2020 | Katharina Ölsböck | The Hole System of Triangulated Shapes |

Thursday, December 5, 2019 | Adam Brown | Persistent Microlocal Geometry |

Wednesday, December 1, 2019 | Vojtěch Kaluža | Colin de Verdiere parameter and representations of graphs |

Wednesday, November 20, 2019 | Alessandro Mella (University of Bologna) | Non-Topological Persistence for Computer Vision |

November 6, 2019 | Raphael Zentner | Irreducible SL(2,C)-representations of integer homology 3-spheres |

30 October, 2019 | Oliver Roche-Newton | Growth, Incidence Bounds and Affine Group Energy |

18 October, 2019 | Ziga Virk | Rips Complexes as Nerves |

4 September, 2019 | Sergey AVVAKUMOV | Envy-free division and degrees of equivariant maps. |

Wednesday, August 14, 2019 | Amir Jafari | On the Chromatic Number of Kneser Graphs and Hypergraphs and Their Variants. |

August 7, 2019 | Moritz Lang | Sandpile monomorphisms and scaling limits |

July 31, 2019 | Burak BUDANUR | Detecting recurrences in high-dimensional flows from persistence |

July 17, 2019 | Adam Brown | Probabilistic Convergence and Stability of Random Mapper Graphs |

June 19, 2019 | Mathijs Wintraecken | Triangulating submanifolds: An elementary and quantified version of Whitney's method |

May 29, 2019 | Csaba Toth | Online Unit Clustering and Covering in Euclidean Space |

May 22, 2019 | Micha Sharir | Polynomials vanishing on Cartesian products: Theory and algorithms |

May 15, 2019 | Patrick Schnider | Ham-Sandwich cuts and center transversals in subspaces |

Wednesday, May 8, 2019 | Mathijs Wintraecken | Triangulating manifolds: An overview with a focus on Riemannian simplices |

April 26, 2019 | Herbert Edelsbrunner | Whence and whither computational topology (part of workshop) |

April 25, 2019 | Gunnar Carlsson | Topological Modelling (part of workshop) |

April 24, 2019 | Uli Bauer, TU Munich | The structure of persistence: an introspection (part of workshop) |

Wednesday, April 17, 2019 | Alan Marcelo ARROYO GUEVARA | What can geometry teach us about topological drawings of graphs? |

Wednesday, April 3, 2019 | Roland Roth. | Interplay of Geometry and Thermodynamics in Physics and Biology |

Wednesday, March 27, 2019 | Chris Hofer | Applying Persistent Homology in Machine Learning |

Wednesday, March 20, 2019 | Ranita Biswas | Relaxed Diophantine Equations for Geometric Primitives in Integer Space |

March 6, 2019 | Emo Welzl | Connectivity of the Flip-Graph of Triangulations |

Wednesday, January 16 2019, 1:00 PM @ Mondi 3 | Rado Fulek | Eliminating Crossings in Drawings of Graphs |

Wednesday, November 14 2018, 1:00 PM @ Mondi 3 | Mehdi Makhul | Probabilities of incidence between lines and a plane curve over finite fields. |

Wednesday, September 12, 1:00 PM @ Mondi 3 | Sergey Avvakumov | Probabilities of incidence between lines and a plane curve over finite fields |

Thursday, August 16, 1:00 PM @ Mondi 3 | Domotor Palvolgyi | Unlabeled compression schemes |

Tuesday, August 14, 1:00 PM @ Mondi 3 | Zur Luria | Simple connectivity in random 2-complexes |

Wednesday, May 30, 1:30 PM @ Mondi 3 | Georg Osang | The Multi-cover Persistence of Euclidean Balls |

Wednesday, May 30, 1:00 PM @ Mondi 3 | Kristof Huszar | On the Treewidth of Triangulated 3-Manifolds |

Wednesday, May 23, 1:00 PM @ Mondi 3 | Mikhail SHKOLNIKOV | Limit of the sandpile group |

Wednesday, April 18, 1:00 PM @ Mondi 3 | Jie Liang | Modeling cell migration and computing exact probability landscape of stochastic networks |

Wednesday, April 11, 1:00 PM @ Meeting room 2nd floor Central Building | Grzegorz Muszynski | Topological Analysis and Machine Learning for Detecting Weather Patterns in Climate Model Output |

Thursday, March 22, 4:00 PM @ Meeting room 2nd floor Central Building | Katharina Ölsböck | The Dynamic Wrap Complex in 2D and 3D |

Wednesday, March 7, 1:00 PM @ Mondi 2 | Sergey Avvakumov | How to turn the sphere inside out and other applications of h-principle. |

TUESDAY, March 6, 2:45 PM @ Mondi 2 | Marian Mrozek | Persistence of Morse Decompositions in finite topological spaces. |

MONDAY, February 5, 2:00PM @ Mondi 3 | Ori Parzanchevski | Random walks on (Ramanujan) graphs and complexes |

Wednesday, January 18 (Thursday), 1:00PM @ Mondi 3 | Alexey Glazyrin (University of Texas Rio Grande Valley) | Sets with few distances |

Wednesday, January 17, 1:00PM @ Mondi 3 | Ivan Izmestiev | Non-polytopal spheres and barycentric subdivisions |

Wednesday, December 20, 1:00PM @ Mondi 3 | Teresa Heiss | Persistent Homology of Rips-complexes of Metric Graphs |

Wednesday, December 13, 1:00PM @ Mondi 3 | Stephan Zhechev | From algebra to geometry: How to represent homotopy group elements as simplicial maps. |

Wednesday, December 6, 1:00PM @ Mondi 3 | Fedor Manin | Geometrically bounded embeddings |

Wednesday, September 13, 1:00PM @ Mondi 3 | Pawel Dlotko | Applied persistent homology |

Wednesday, August 23, 1:00PM @ Mondi 3 | Nora Frankl | On equilateral sets in subspaces of l_\infty^n |

Wednesday, August 16, 12:45PM @ Mondi 3 | Teresa Heiss | Streaming Algorithm for Euler Characteristic Curves of Multidimensional Images |

Wednesday, July 5, 12:45PM @ Mondi 3 | Vojtech Kaluza | Mapping n grid points onto a square forces an arbitrarily large Lipschitz constant |

Wednesday, June 28, 12:45PM @ Mondi 3 | Edgardo Roldan-Pensado | On the colourful Helly theorem |

Wednesday, June 21, 12:45PM @ Mondi 3 | Stephan Zhechev | From algebra to geometry: How to represent homotopy group elements as simplicial maps. |

Wednesday, June 14, 12:45PM @ Mondi 3 | Ziga Virk | Intrinsic persistence of geodesic spaces |

Wednesday, June 7, 12:45PM @ Mondi 3 | Arseniy Akopyan | What figures on the second floor are about. |

Wednesday, April 12, 12:45PM @ Mondi 3 | Bruno Levi | Voronoi Story: To L-infinity and beyond |

Wednesday, March 29, 12:45PM @ Mondi 3 | Alessandro Chiancone (Know Center TU Graz) | Dimensionality reduction: a chat on Sliced Inverse Regression |

Wednesday, February 22, 12:45PM @ Mondi 3 | Arnaud de Mesmay | On the complexity of optimal homotopies in two dimensions. |

Wednesday, February 8, 12:45PM @ Mondi 3 | Mikhail Skopenkov | Discrete field theory and cochain products |

Wednesday, January 25, 12:45PM @ Mondi 3 | Reinhold G. Erben | Interaction between bone structure and hormones |

Wednesday, January 18, 12:45 am @ Mondi 3 | Pratyush Pranav | Persistent Holes in the Universe : A (hierarchical) topology of the cosmic mass distribution |

Wednesday, December 14, 12:45 am @ Mondi 3 | Andrey Bondarenko | Strongly regular graphs and Borsuk's conjecture |

Monday, December 12, 11:00 am @ Mondi 3 | Alexander Plakhov | Invisible bodies with specular surface |

Wednesday November 23, 12:45 pm @ Mondi 3 | Zuzana Patakova | Colorful simplicial depth |

Wednesday November 9, 12:45 pm @ Mondi 3 | Pavel Patak | Generalizing Heawood inequalities for manifolds |

Wednesday October 12, 12:45 pm @ Mondi 3 | Fedor Petrov (Steklov Institute of Mathematics, St. Petersburg) | Combinatorics of the Lipschitz polytope |

Wednesday August 25, 12:45 pm @ Mondi 3 | Arkadiy Skopenkov | Stability of intersections of paths in the plane and the van Kampen obstruction |

Thursday August 18, 13:15 pm @ Mondi 3 | Jeremy Mason | Statistical Topology of the Grain Growth Microstructure |

Wednesday August 17, 12:45 pm @ Mondi 3 | Roman Karasev | Center transversal theorem with improved transversal depth |

August 10, 12:45 pm @ Mondi 3 | Moshe White | Types of Tverberg partitions |

Wednesday, 13 April 2016, 12:45 @ Mondi 3 | Alexey Balitskiy | Shortest closed billiard trajectories in convex bodies: Elementary techniques in non-elementary problems. |

Wednesday, 24 February 2015, 12:45 @ Mondi 3 | Imre Barany | On a geometric Ramsey number |

Wednesday, 16 December 2015, 13:15 @ Mondi 3 | Peter Franek | Robust satisfiability of nonlinear systems |