Events in November–December 2019
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October 28, 2019
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October 29, 2019
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October 30, 2019
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October 31, 2019
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NovemberNovember 1, 2019 |
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November 3, 2019
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November 4, 2019
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November 5, 2019
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November 6, 2019
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November 7, 2019
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November 8, 2019
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November 9, 2019
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November 10, 2019
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November 11, 2019
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November 12, 2019
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November 13, 2019
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November 14, 2019(1 event) Prophet Inequalities for I.I.D. Random Variables from an Unknown Distribution by Paul Duetting (Google, switzerland) – (ACM EC 2019 Best Full Paper Award) A central object in optimal stopping theory is the single-choice prophet inequality for independent, identically distributed random variables: given a sequence of random variables X1,..., Xn drawn independently from a distribution F, the goal is to choose a stopping time τ so as to maximize α such that for all distributions F we have E[Xτ] ≥ α · E[maxt Xt]. What makes this problem challenging is that the decision whether τ = t may only depend on the values of the random variables X1,..., Xt and on the distribution F. For a long time the best known bound for the problem had been α ≥ 1 − 1/e ≈ 0.632, but quite recently a tight bound of α ≈ 0.745 was obtained. The case where F is unknown, such that the decision whether τ = t may depend only on the values of the random variables X1,..., Xt, is equally well motivated but has received much less attention. A straightforward guarantee for this case of α ≥ 1/e ≈ 0.368 can be derived from the solution to the secretary problem, where an arbitrary set of values arrive in random order and the goal is to maximize the probability of selecting the largest value. We show that this bound is in fact tight. We then investigate the case where the stopping time may additionally depend on a limited number of samples from F , and show that even with o(n) samples α ≤ 1/e. On the other hand, n samples allow for a significant improvement, while O(n2) samples are equivalent to knowledge of the distribution: specifically, with n samples α ≥ 1 − 1/e ≈ 0.632 and α ≤ ln(2) ≈ 0.693, and with O(n2) samples α ≥ 0.745 − ϵ for any ϵ > 0. Joint work with Jose Correa (Universidad de Chile), Felix Fischer (Queen Mary), and Kevin Schewior (ENS Paris) Bâtiment IMAG (442) |
November 15, 2019
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November 16, 2019
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November 17, 2019
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November 18, 2019
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November 19, 2019
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November 20, 2019
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November 21, 2019(1 event) Understanding and improving the performance of applications on NUMA systems by Vivien Quema (LIG) – Understanding and improving the performance of applications on NUMA systems Modern multicore systems are based on a Non-Uniform Memory Access (NUMA) design. Efficiently exploiting such architectures is notoriously complex. In this talk we will present different works we did during these last years to help application and system designers leveraging the power of these architectures. In particular, we will present some profiling tools that we used to detect inefficiencies and some algorithms/heuristics that we implemented within the Linux kernel to improve the performance of NUMA systems. Bâtiment IMAG (442) |
November 22, 2019
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November 23, 2019
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November 24, 2019
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November 25, 2019
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November 26, 2019
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November 27, 2019
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November 28, 2019(1 event) Back from Supercomputing by Bruno Raffin (Datamove) – Bruno will present his report from the new trends he saw this year at supercomputing as well as explain some technical talks he liked presented at the conference. Bâtiment IMAG (442) |
November 29, 2019
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November 30, 2019
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DecemberDecember 1, 2019 |
December 2, 2019
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December 3, 2019
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December 4, 2019
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December 5, 2019(1 event) Keynote: Flandrin – |
December 6, 2019
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December 7, 2019
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December 8, 2019
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December 9, 2019
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December 10, 2019
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December 11, 2019(1 event) Phd Defense: Autonomic Resilience of Distributed IoT Applications in the Fog, by Umar Ozeer (Polaris) – Abstract: The Fog, however, is unstable because it is constituted of billions of heterogeneous devices in a dynamic ecosystem. IoT devices may regularly fail because of bulk production and cheap design. Moreover, the Fog-IoT ecosystem is cyber-physical and thus devices are subjected to external physical world conditions which increase the occurrence of failures. When failures occur in such an ecosystem, the resulting inconsistencies in the application affect the physical world by inducing hazardous and costly situations. In this Thesis, we propose an end-to-end autonomic failure management approach for IoT applications deployed in the Fog. The proposed approach recovers from failures in a cyber-physical consistent way. Cyber-physical consistency aims at maintaining a consistent behavior of the application with respect to the physical world, as well as avoiding dangerous and costly circumstances. The approach was validated using model checking techniques to verify important correctness properties. It was then implemented as a framework called F3ARIoT. This framework was evaluated on a smart home application. The results showed the feasibility of deploying F3ARIoT on real Fog-IoT applications as well as its good performances in regards to end user experience. Bâtiment IMAG Saint-Martin-d'Hères, 38400 France |
December 12, 2019
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December 13, 2019
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December 14, 2019
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December 15, 2019
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December 16, 2019
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December 17, 2019
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December 18, 2019
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December 19, 2019(1 event) Tropical approach to semidefinite programming and mean payoff games, by Mateusz Skomra (ENS Lyon) – Semidefinite programming (SDP) is a fundamental tool in convex and polynomial optimization. It consists in minimizing linear functions over spectrahedra (sets defined by linear matrix inequalities). In particular, SDP is a generalization of linear programming. In this talk, we discuss the nonarchimedean analogue of SDP, replacing the field of real numbers by the field of Puiseux series. Our methods rely on tropical geometry and, in particular, on the study of tropicalization of spectrahedra. We show that, under genericity conditions, tropical spectrahedra encode Shapley operators associated with stochastic mean payoff games. As a result, a large class of semidefinite feasibility problems defined over Puiseux series can be solved efficiently using combinatorial algorithms designed for stochastic games. Conversely, we use tropical spectrahedra to introduce a condition number for stochastic mean payoff games. We show that this conditioning controls the number of value iterations needed to decide whether a mean payoff game is winning. In particular, we obtain a pseudopolynomial bound for the complexity of value iteration provided that the number of random positions is fixed. Bâtiment IMAG (442) |
December 20, 2019(1 event) HDR defense of Panayotis Mertikopoulos (Polaris) – Online optimization and learning in games: Theory and applications HDR Jury: The traditional "pot de soutenance" will take place right after the defense at the ground floor of the IMAG building. Bâtiment IMAG (amphitheater) Saint-Martin-d'Hères, 38400 France |
December 21, 2019
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December 22, 2019
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December 23, 2019
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December 24, 2019
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December 25, 2019
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December 26, 2019
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December 27, 2019
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December 28, 2019
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December 29, 2019
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December 30, 2019
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December 31, 2019
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JanuaryJanuary 1, 2020 |
January 2, 2020
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January 3, 2020
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January 4, 2020
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January 5, 2020
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