Calendar

Events in October–November 2022

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September 26, 2022
September 27, 2022
September 28, 2022
September 29, 2022
September 30, 2022

October

October 1, 2022
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October 11, 2022
October 12, 2022(1 event)

Seminar Joao Comba: Data Visualization for The Understanding of COVID-19

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October 12, 2022

Title: Data Visualization for The Understanding of COVID-19
 
Speaker: Joao Comba (UFRGS)
 
Abstract: In this talk, I will describe several data visualization
projects related to COVID-19 data analysis. The first work describes
an analysis tool for comparing the evolution of COVID-19
data in different regions worldwide. The main component of our tool is
a similarity engine that searches for similar patterns of COVID-19 time
series and a storytelling dashboard that identifies the waves of COVID-
19. We also introduce a new type of difference plot that allows a more
straightforward comparison of time series evolution. The second work
leverages the big-data infrastructure we developed for real-time
analysis to study two years of clinical admissions in the public health
system of Brazil, composed of more than 100 million records. The third
work is related to the diagnosis of COVID-19 from computed tomography
and clinical data. We will describe COVID-VR, a novel approach for
classifying pulmonary diseases based on volume rendering images of the
lungs taken from different angles, thus providing a global view of the
entire lung in each image. I will conclude the talk with a summary of
my current research projects.
 
Short-bio: João L. D. Comba is a Full Professor at the Instituto de
Informática at UFRGS, where he conducts research activities,
undergraduate and graduate education, and supervises doctoral,
master, and scientific initiation students. He holds a Ph.D. in
Computer Science from Stanford University, United States. 2000. His
research areas include data visualization and analysis, data science,
geometric algorithms, and spatial data structures. He is currently co-
chair of the Visualization Corner of the Journal Computing in Science &
Engineering and associate editor of the Computer & Graphics Journal. 

Bâtiment IMAG (442)
Saint-Martin-d'Hères, 38400
France
View Location
Map Bâtiment IMAG (442)
October 13, 2022(1 event)

Séminaire Antoine Oustry: Polynomial optimization for parameterizing dynamical systems

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October 13, 2022

Polynomial optimization for parameterizing dynamical systems

Abstract: We consider a polynomial dynamical system that depends on some tunable parameters. We raise the question of how to configure this system optimally, in terms of costs and stability.
More precisely, we will give an overview of polynomial optimization approaches to
(a) find a (stable) equilibrium point of the dynamical system that minimizes a polynomial function
(b) approximate regions of stability around the equilibrium points.
We illustrate our work with some applications in power engineering.
October 14, 2022
October 15, 2022
October 16, 2022
October 17, 2022
October 18, 2022
October 19, 2022
October 20, 2022(1 event)

Séminaire Philippe Swartvagher (Inria Bordeaux): Possible interactions between task-based runtime systems and communication libraries

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October 20, 2022

Titre : Possible interactions between task-based runtime systems and communication libraries

Abstract :

The increasing complexity of supercomputers leads to the emergence of task-based runtime systems, to exploit more easily the performance they can offer. These runtime systems usually rely on a third-party library to perform communications (following the MPI standard, for instance) when they are used in a distributed fashion. In this presentation, I will summarize my work during my PhD about possible interactions between task-based runtime systems and communication libraries. The interactions can be positive, for instance improving the performance by detecting and executing broadcasts in a smart way; or negative and hurting the application performance, for instance because of contention between communications and computations. I will also mention some results regarding the tracing system used to analyze executions: the sources of overhead and the problem of accurate clock synchronization.
October 21, 2022
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October 25, 2022
October 26, 2022
October 27, 2022(1 event)

Seminar Bryce Ferguson: "Information and Influence: Overcoming and Exploiting Uncertainty in Congestion Games"

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October 27, 2022

Title: Information and Influence: Overcoming and Exploiting Uncertainty in Congestion Games
Abstract: In large-scale, socio-technical systems (such as traffic networks, power grids, supply chains, etc.) the operating efficiency depends heavily on the actions of human users. It is well known that when users act in their own self-interest, system performance can be sub-optimal. Our capabilities in alleviating this inefficiency rely on our knowledge of user decision making and various system parameters. In this talk, I will present two settings where information affects our ability to influence system performance. In the first, we consider designing monetary incentives for players in a congestion game without exact knowledge of users’ price-sensitivity or path latency-characteristics; we provide a comparison of the effectiveness of different incentive types and quantify the value of different pieces of information. In the second, we consider a flipped paradigm, where the system operator has more information about system parameters than the users and can selectively reveal pertinent information. We show, in the context of Bayesian-congestion games, that signaling information to users has the opportunity to improve system performance but also the capability to make performance worse than if no information were shared at all. We then show the advantages of concurrently using monetary incentives and information signals by providing bounds on the benefit to system performance and methods to find optimal mechanisms of each type.
Bâtiment IMAG (406)
Saint-Martin-d'Hères, 38400
France
Map Bâtiment IMAG (406)
October 28, 2022
October 29, 2022
October 30, 2022
October 31, 2022

November

November 1, 2022
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November 9, 2022
November 10, 2022(1 event)

Verimag seminar: Stephan Plassart

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November 10, 2022

Total Flow Analysis (TFA) is a method for conducting the worst-case analysis of time sensitive networks without cyclic dependencies. In networks with cyclic dependencies, Fixed-Point TFA introduces artificial cuts, analyses the resulting cycle-free network with TFA, and iterates. If it converges, it does provide valid performance bounds. We show that the choice of the specific cuts used by Fixed-Point TFA does not affect its convergence nor the obtained performance bounds, and that it can be replaced by an alternative algorithm that does not use any cut at all, while still applying to cyclic dependencies.

Room: 206

Bâtiment IMAG (206)
November 11, 2022
November 12, 2022
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November 15, 2022
November 16, 2022
November 17, 2022(1 event)

Seminar Olivier Bilenne

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November 17, 2022

Solutions of Poisson's equation for first-policy improvement in parallel queueing systems
This talk addresses the problem of (state-aware) job dispatching at minimum long-run average cost in a parallel queueing system with Poisson arrivals. Policy iteration is a technique for approaching optimality through improvement of an initial dispatching policy. Its implementation rests on the computation of value functions. In this context, we will consider the M/G/1-FCFS queue endowed with an arbitrary cost function for the waiting times of the incoming jobs. The associated relative value function is a solution of Poisson's equation for Markov chains, which I propose to solve in the Laplace transform domain by considering an ancillary stochastic process extended to (imaginary) negative backlog states. This construction enables us to issue closed-form solutions for simple cost functions (polynomial, exponential, and their piecewise compositions), in turn permitting the derivation of interval bounds for the relative value functions to more general cost functions. Such bounds allow for an exact implementation of the first improvement step of policy iteration in a parallel queueing system.
One objective of the talk is to identify the main obstacles to the implementation of the policy iteration algorithm in parallel queueing systems; the purpose then to discuss the new directions that transform domain analysis might offer beyond first policy improvement.
Further reading: Olivier Bilenne. Dispatching to parallel servers: solutions of Poisson's equation for first-policy improvement. Queueing Systems, Springer Verlag, 2021, Queueing Systems, 99 (3), pp.199-230. https://hal.archives-ouvertes.fr/hal-02925284
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November 30, 2022

December

December 1, 2022(1 event)

Séminaire Stephane Durand

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December 1, 2022

Jeux de contagions et d'influences: les différentes formes, les approches et le contexte
December 2, 2022
December 3, 2022
December 4, 2022

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