Reclaiming the energy of a schedule: models and algorithms

We consider a task graph to be executed on a set of processors. We assume that the mapping is given, say by an ordered list of tasks to execute on each processor, and we aim at optimizing the energy consumption while enforcing a prescribed bound on the execution time. While it is not possible to change the allocation of a task, it is possible to change its speed. Rather than using a local approach such as backfilling, we consider the problem as a whole and study the impact of several speed variation models on its complexity. For continuous speeds, we give a closed-form formula for trees and series-parallel graphs, and we cast the problem into a geometric programming problem for general directed acyclic graphs. We show that the classical dynamic voltage and frequency scaling (DVFS) model with discrete modes leads to a NP-complete problem, even if the modes are regularly distributed (an important particular case in practice, which we analyze as the incremental model). On the contrary, the VDD-hopping model leads to a polynomial solution. Finally, we provide an approximation algorithm for the incremental model, which we extend for the general DVFS model.Comment: A two-page extended abstract of this work appeared as a short presentation in SPAA'2011, while the long version has been accepted for publication in "Concurrency and Computation: Practice and Experience

On the development of the Echinidæ

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Two approximation algorithms for bipartite matching on multicore architectures

International audienceWe propose two heuristics for the bipartite matching problem that are amenable to shared-memory parallelization. The first heuristic is very intriguing from a parallelization perspective. It has no significant algorithmic synchronization overhead and no conflict resolution is needed across threads. We show that this heuristic has an approximation ratio of around 0.632 under some common conditions. The second heuristic is designed to obtain a larger matching by employing the well-known Karp-Sipser heuristic on a judiciously chosen subgraph of the original graph. We show that the Karp-Sipser heuristic always finds a maximum cardinality matching in the chosen subgraph. Although the Karp-Sipser heuristic is hard to parallelize for general graphs, we exploit the structure of the selected subgraphs to propose a specialized implementation which demonstrates very good scalability. We prove that this second heuristic has an approximation guarantee of around 0.866 under the same conditions as in the first algorithm. We discuss parallel implementations of the proposed heuristics on a multicore architecture. Experimental results, for demonstrating speed-ups and verifying the theoretical results in practice, are provided

Brief Announcement: Reclaiming the Energy of a Schedule, Models and Algorithms

Version longue publiée dans Concurrency and Computation: Practice and Experience.International audienceWe consider a task graph to be executed on a set of processors. We assume that the mapping is given, say by an ordered list of tasks to execute on each processor, and we aim at optimizing the energy consumption while enforcing a prescribed bound on the execution time. While it is not possible to change the allocation of a task, it is possible to change its speed. We study the complexity of the problem for different models: continuous speeds, discrete modes, distributed either arbitrarily or regularly, and VDD-hopping

Microbial Production of Food Grade Pigments

Već se godinama raspravlja o kontroverznoj temi sintetskih bojila u hrani. Danas potrošači strogo i negativno ocijenjuju njihovu prisutnost u hrani pa je sve veće zanimanje za upotrebom prirodnih alternativnih bojila. Priroda je bogata bojama (minerali, biljke, mikroalge, itd.) i puna mikroorganizama koji proizvode pigmente (plijesni, kvasci i bakterije). Mikroorganizmi proizvode molekule poput karotenoida, melanina, flavina, kinona, te posebice monascina, violaceina ili indiga. Uspjeh bilo kojeg pigmenta proizvedenog fermentacijom ovisi o njegovoj prihvatljivosti na tržištu, zakonskoj regulativi i veličini kapitalnih ulaganja. Prije nekoliko godina izražena je sumnja u to da se pigmenti hrane dobiveni fermentacijom mogu uspješno komercijalizirati zbog velikih ulaganja u fermentacijska postrojenja te dugih i opsežnih toksikoloških studija što zahtijevaju regulatorne agencije. Također se mora uzeti u obzir i percepcija javnosti o biotehnološkim proizvodima. Neki od pigmenata hrane proizvedenih fermentacijom danas su prisutni na tržištu: Monascus pigmenti, astaksantin iz Xanthophyllomyces dendrorhous, Arpink Red iz Penicillium oxalicum, riboflavin iz Ashbya gossypii, b-karoten iz Blakeslea trispora. Pigmenti iz algi ili biljaka, koji se koriste kao bojila za namirnice ili dodatak hrani, mogu se uspješno plasirati na tržište, gdje potrošači mogu izdvojiti više za potpuno prirodnu hranu.The controversial topic of synthetic dyes in food has been discussed for many years. The scrutiny and negative assessment of synthetic food dyes by the modern consumer have raised a strong interest in natural colouring alternatives. Nature is rich in colours (minerals, plants, microalgae, etc.), and pigment-producing microorganisms (fungi, yeasts, bacteria) are quite common. Among the molecules produced by microorganisms are carotenoids, melanins, flavins, quinones, and more specifically monascins, violacein or indigo. The success of any pigment produced by fermentation depends upon its acceptability on the market, regulatory approval, and the size of the capital investment required to bring the product to market. A few years ago, some expressed doubts about the successful commercialization of fermentation-derived food grade pigments because of the high capital investment requirements for fermentation facilities and the extensive and lengthy toxicity studies required by regulatory agencies. Public perception of biotechnology-derived products also had to be taken into account. Nowadays some fermentative food grade pigments are on the market: Monascus pigments, astaxanthin from Xanthophyllomyces dendrorhous, Arpink Red from Penicillium oxalicum, riboflavin from Ashbya gossypii, b-carotene from Blakeslea trispora. The successful marketing of pigments derived from algae or extracted from plants, both as a food colour and a nutritional supplement, reflects the presence and importance of niche markets in which consumers are willing to pay a premium for »all natural ingredients«

FORMER LES FUTURS PROFESSEURS DE LETTRES MODERNES À L’ANGLAIS. QUELSENJEUX ?/ WHYSHOULD WE TEACH ENGLISH TO FUTURE TEACHERS OF FRENCH IN FRANCE?

La formation professionnelle des enseignants de l’enseignement secondaire est au cœur de la prochaine réforme qui est opérationnelle depuis septembre 2021 en France. Les Instituts nationaux supérieurs du professorat et de l’éducation doivent à nouveau penser leur offre de formation en fonction de l’évolution du métier, des besoins des élèves et des directives européennes. Dans cet article, nous nous posons la question du bien-fondé d’un enseignement en anglais pour les futurs professeurs de Lettres modernes dans leur cursus de formation initiale

Une comparaison des algorithmes d'apprentissage pour la survie avec donn\'ees manquantes

Survival analysis is an essential tool for the study of health data. An inherent component of such data is the presence of missing values. In recent years, researchers proposed new learning algorithms for survival tasks based on neural networks. Here, we studied the predictive performance of such algorithms coupled with different methods for handling missing values on simulated data that reflect a realistic situation, i.e., when individuals belong to unobserved clusters. We investigated different patterns of missing data. The results show that, without further feature engineering, no single imputation method is better than the others in all cases. The proposed methodology can be used to compare other missing data patterns and/or survival models. The Python code is accessible via the package survivalsim. -- L'analyse de survie est un outil essentiel pour l'\'etude des donn\'ees de sant\'e. Une composante inh\'erente \`a ces donn\'ees est la pr\'esence de valeurs manquantes. Ces derni\`eres ann\'ees, de nouveaux algorithmes d'apprentissage pour la survie, bas\'es sur les r\'eseaux de neurones, ont \'et\'e con\c{c}us. L'objectif de ce travail est d'\'etudier la performance en pr\'ediction de ces algorithmes coupl\'es \`a diff\'erentes m\'ethodes pour g\'erer les valeurs manquantes, sur des donn\'ees simul\'ees qui refl\`etent une situation rencontr\'ee en pratique, c'est-\`a dire lorsque les individus peuvent \^etre group\'es selon leurs covariables. Diff\'erents sch\'emas de donn\'ees manquantes sont \'etudi\'es. Les r\'esultats montrent que, sans l'ajout de variables suppl\'ementaires, aucune m\'ethode d'imputation n'est meilleure que les autres dans tous les cas. La m\'ethodologie propos\'ee peut \^etre utilis\'ee pour comparer d'autres mod\`eles de survie. Le code en Python est accessible via le package survivalsim.Comment: in French languag

Y a-t-il analogie entre les opérations sous-jacentes aux constructions V ØNs et VPA ?

The question here is to know whether the structure V ØNs (he was taking Ønotes) corresponds with the traditional scheme V + C1 or whether it can be compared with a phrasal verb (go up). Such a problem means calculating the constitutive properties of N and V from an enunciative point of view, studying minimal pairs of dependent elements and their influence on each other. A detailed analysis will show many similarities between V ØNs and VPA and its limitations as well