March 10, 2022
Polaris-tt: Kimang Khun: computing index policies for restless bandits
Polaris-tt: Kimang Khun: computing index policies for restless bandits
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March 10, 2022
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News
- Journée au vert POLARIS 2022/05/23
- DATAMOVE/POLARIS picnic 2021/06/22
- DATAMOVE/POLARIS BBQ 2019 2019/06/14
- POLARIS Bootcamp (May 2019) 2019/05/24
- slides of Andras Gyorgy 2016/01/15
Next seminars
Events
Events in March–April 2022
MMonday TTuesday WWednesday TThursday FFriday SSaturday SSunday 28February 28, 2022March
1March 1, 20222March 2, 2022Polaris-tt: Chen Yan: restless bandits and LP-relaxations
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March 3, 20224March 4, 20225March 5, 20226March 6, 20227March 7, 20228March 8, 20229March 9, 2022Polaris-tt: Kimang Khun: computing index policies for restless bandits
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March 10, 202211March 11, 202212March 12, 202213March 13, 202214March 14, 202215March 15, 202216March 16, 2022Polaris-tt: Till Kletti (Introducing the expohedron for fair and useful rankings)
Seminar Bruno Raffin (Large Scale Data Assimilation)
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March 17, 2022Title: Large Scale Data Assimilation
Authors: Sebastian Friedemann and Bruno Raffin
Abstract:
How to combine data, which may be available though different sensors,
with traditional numerical solvers designed to compute solutions of
PDEs modeling complexe phenomenon ? Bridging both is a timely
question with the multiplication of data sources (IoT). But
augmenting solvers working in high dimension spaces with external
data is far from trivial. Both are usually subject to uncertainties.
Data Assimilation (DA) is a well known approach to address this issue. DA is actually
routinely used in production for weather forecast for instance. In this talk, I will first motivate and
introduce the principles of Data Assimilation, including the
different families of techniques (statistical, variational) with a
specific focus on statistical ones (EnKF and particle filter).
From there, I will explain the worked performed with the
Melissa framework to support very large scale statistical data
assimilation with the EnKF method. We will dive into the details
of the software infrastructure that has been designed to go to very large scale,
supporting features like elasticity, fault tolerance and dynamics
load balancing, and show some experimental performance results.18March 18, 202219March 19, 202220March 20, 202221March 21, 202222March 22, 202223March 23, 2022Polaris-tt: Victor Boone (title to be annouced)
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March 24, 2022Polaris-datamove seminar: Georges Da Costa (Multi-objective resources optimization Performance- and Energy-aware HPC and Clouds)
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March 24, 2022Titre: "Multi-objective resources optimization Performance- and Energy-aware HPC and Clouds"
This talk will answer to the challenge "How to efficiently manage a datacenter ?" by providing theoretical and practical tools.
Datacenters are at the center of the life of an increasing part of the world population while being mostly unknown: From online services to weather forcast. Their role, while transparent, is of the utmost importance. Their electricity consumption is then a key challenge, and will be even more in a near future. Managing efficiently leads to optimization of quality of service, but also to improving energy efficiency.
This talk will show the required tools: The tools linked to measures and monitoring, from a technical point of view, but also by the definition of metrics. Then, it will explore methods to model such problems, along with direct or approximated resolution techniques. The next step will show several heuristics to quickly reach approximated solutions. Several types of validations, from experimental to improved simulated ones will serve as support for this talk.
25March 25, 202226March 26, 202227March 27, 202228March 28, 202229March 29, 202230March 30, 2022Seminar Bertrand Simon (An Exact Algorithm for the Linear Tape Scheduling Problem)
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March 31, 2022Title: An Exact Algorithm for the Linear Tape Scheduling Problem
Abstract: Magnetic tapes are often considered as an outdated storage technology, yet they are still used to store huge amounts of data. Their main interests are a large capacity and a low price per gigabyte, which come at the cost of a much larger file access time than on disks. With tapes, finding the right ordering of multiple file accesses is thus key to performance. Moving the reading head back and forth along a kilometer long tape has a non-negligible cost and unnecessary movements thus have to be avoided. However, the optimization of tape request ordering has then rarely been studied in the scheduling literature, much less than I/O scheduling on disks. For instance, minimizing the average service time for several read requests on a linear tape remains an open question. Therefore, in this paper, we aim at improving the quality of service experienced by users of tape storage systems, and not only the peak performance of such systems. To this end, we propose a reasonable polynomial-time exact algorithm while this problem and simpler variants have been conjectured NP-hard. We also refine the proposed model by considering U-turn penalty costs accounting for inherent mechanical accelerations. Then, we propose a low-cost variant of our optimal algorithm by restricting the solution space, yet still yielding an accurate suboptimal solution. Finally, we compare our algorithms to existing solutions from the literature on logs of the mass storage management system of a major datacenter. This allows us to assess the quality of previous solutions and the improvement achieved by our low-cost algorithm. Aiming for reproducibility, we make available the complete implementation of the algorithms used in our evaluation, alongside the dataset of tape requests that is, to the best of our knowledge, the first of its kind to be publicly released.
April
1April 1, 20222April 2, 20223April 3, 20224April 4, 20225April 5, 20226April 6, 2022Polaris-tt: Achile Baucher: le modèle World3
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April 7, 20228April 8, 20229April 9, 202210April 10, 202211April 11, 202212April 12, 202213April 13, 2022Polaris-tt: Rémi Castera - Statistical discrimination in Stable Matchings
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April 14, 202215April 15, 202216April 16, 202217April 17, 202218April 18, 202219April 19, 202220April 20, 202221April 21, 202222April 22, 202223April 23, 202224April 24, 202225April 25, 202226April 26, 202227April 27, 2022Polaris-tt: Victor Leger – A large dimensional analysis of multi-task semi-supervised classification
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April 28, 2022Seminar by Martin Schreiber (LJK, Airsea)
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April 28, 2022Title: A Brief Glimpse on Emerging Time Integration Methods for Weather and Climate Simulations
Speaker: Martin Schreiber
Abstract:
Weather and climate simulations face new challenges due to changes in computer architectures caused by physical limitations. From a pure computing perspective, algorithms are required to cope with stagnating or even decreasing per-core speed and increasing on-chip parallelism. These trends will continue and already led to research on partly disruptive mathematical and algorithmic reformulations of dynamic cores, e.g., using (additional) parallelism along the time dimension.
This presentation provides an overview and introduction of a variety of promising newly developed and evaluated time integration methods for equations related to prototypical dynamical cores, all aimed at improving the ratio of wall clock time vs. error: Rational Approximation of Exponential Integration (REXI), Parallel Full Approximation Scheme in Space and Time (PFASST) and Semi-Lagrangian methods combined with Parareal. We get improved time-vs.-error rates, but sometimes with additional challenges on the way which needs to be further overcome. Overall, our results motivate further investigation and combination of these methods for operational weather/climate systems.
I gratefully acknowledge collaborators related to this presentation
Jed Brown, Finn Capelle, François Hamon, Terry Haut, Richard Loft, Michael Minion, Matthew Normile, Nathanael Schaeffer, Andreas Schmitt, Pedro S. Peixoto, Raphael Schilling29April 29, 202230April 30, 2022May
1May 1, 2022Meta
