Meetings & Seminars

Seminar

Currently, our seminar takes place virtually on our private BigBlueButton server : contact us if you want to participate to the live with an audio/video exchange with the lecturer or to private sessions.

Live

You can follow non private sessions of our seminar (and participate through a chat) as well as some other events on our live channel.

Next sessions :

21 January 2022 – 13:30  : Grace Younes – PhD defense

Computation of the L-infinity-norm of finite-dimensional linear systems

Abstract

In this dissertation, we study the computation of the L∞-norm of finite-dimensional linear time-invariant systems. This problem is first reduced to the computation of the maximal y-projection of the real solutions (x, y) of a bivariate polynomial equations system Σ = {P = 0, ∂P/∂x = 0}, where P ∈ Z[x, y]. Then, we use standard computer algebra methods to solve this problem. In particular, we alternatively study a method based on rational univariate representations, a method based on root separation, and finally, a method first based on the sign variation of the leading coefficients of a signed subresultant sequence (Sturm-Habicht) and on the identification of an isolating interval for the maximal y-projection of the real solutions of Σ. We then compute the worst-case bit complexity of each method and compare their theoretical behavior. We also implement each method in Maple and compare their practical behavior (average complexity). A generalization of the above algorithms is finally proposed to the case where the polynomial P also depends on a set of parameters α = [α1,…, αd] ∈ R^d. To do that, we solve the problem using the notion of the Cylindrical Algebraic Decomposition, well-known in algebraic geometry.

25 January 2022 – 14:00 (OURAGAN seminar) : Martin Deraux

Domaines fondamentaux approximatifs en géométrie hyperbolique complexe.
Abstract: J’expliquerai quelques techniques géométriques qui permettent
d’obtenir des domaines fondamentaux approximatifs pour l’action de
certaines classes de groupes discrets d’isométries du plan
hyperbolique complexe. L’objectif principal de l’exposé sera de faire
un panorama des outils calculatoires qui apparaissent dans ce sujet,
et de présenter quelques problèmes qui restent encore difficiles à
résoudre. 

 

Past sessions

14 January 2022 (AFRIMath seminar) : Antonio Lerario (Sissa, Trieste) – Convex bodies in real algebraic geometry

14 January 2022 (AFRIMath seminar) : Birou Lawalé CHITOU (Universté d’Abomey-Calavi – Cotonou) – Otto’s metric of location-scale model is a warped Riemannian metric

3 June 2021 – 15:00 (OURAGAN seminar) : Daniel Robertz – An introduction to Janet bases and Thomas decomposition. replay.

27 May 2021 – 15:00 (OURAGAN seminar) : Laurent Busé – Determinantal tensor product surfaces and the method of moving quadrics. replayslides

21 may 2021 – 11:30 (AFRIMath seminar) :  Aziz Diop (Université Cheikh Anta Diop, Dakar) – K-systoles sur un Schottky. replay

21 may 2021 – 10:30 (AFRIMath seminar) :: Cyriaque Atindogbé (Université Abomey Calavi, Cotonou) – Rigged structure : A bridge between Null and Riemannian Geometries. replay

20 may 2021 – 15:00 (OURAGAN seminar) : Boulos El Hilany: Computing efficiently the non-properness set of polynomial maps on the plane. replayslides.

6 may 2021 – 15:00 (OURAGAN seminar) : Josué Tonelli-Cueto: A numerical algorithm for zero counting. IV: An adaptive speedup. replay

29 april 2021 – 15:00 (OURAGANseminar) : Georges Le Vey, On transcendantal/polynomial equations appearing in the design of musical wind instruments.replay

23 april 2021 – 10:30 (AFRIMath seminar) : Marie-Françoise Roy, Comment calculer la topologie d’une courbe algébrique réelle ?. replay

23 april 2021 – 11:30 (AFRIMath seminar) : Winnie Ossete (Brazzaville), une introduction aux amibes. replay

22 april 2021 – 13:00 (OURAGAN seminar) : Felipe Cucker, Functional Norms, Condition Numbers, and Numerical Algebraic Geometry. replay

15 april 2021 – 15:00 (OURAGAN seminar): Elias Tsigaridas, Solving sparse polynomial systems with sparse Groebner basis. replay

8 april 2021 – 15:00 (OURAGAN seminar): Monique Teillaud, Triangulations de Delaunay de surfaces hyperboliques. replay –  slides

1 april 2021 – 15:00 : private session on triangulation-fibration

25 Mars 2021 – 15:00 : private session (visit of INRIA’s DGD-S)

23 Mars 2021 – 10:00 : private session (computations related to character varieties)

18 Mars 2021 – 15:00(OURAGANseminar): M. Barakat, guided tour of HomAlg. replay.

11 mars 2021 – 15:00 (OURAGAN seminar): M. Wintraecken, Topologically correct PL-approximations of isomanifolds. replayslides

18 Février 2021 – 15:00 (OURAGANseminar): M. Barakat, Organising computer algebra using category theory. – replayslides

11 Février 2021- 15:00 : (private) workshop on triangulated varieties

4 Février 2021 – 15:00 : (private) workshop on mesh

21 Janvier 2021 – 15:00 (OURAGAN seminar) :Clément Maria – Parameterized Complexity of Quantum Knot Invariants – replay – slides.

21 Janvier 2021 – 11:00 (DATASHAPE seminar): Antonin Guilloux & Guillaume Moroz – Visualization of the 8-knot complement fibration – replay – slides.

14 Janvier 2021 – 15:00 (OURAGAN seminar:  Yves Guiraud – Présentations cohérentes des monoïdes d’Artin – replay – slides.

 

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