238 research outputs found
Scalable First-Order Methods for Robust MDPs
Robust Markov Decision Processes (MDPs) are a powerful framework for modeling
sequential decision-making problems with model uncertainty. This paper proposes
the first first-order framework for solving robust MDPs. Our algorithm
interleaves primal-dual first-order updates with approximate Value Iteration
updates. By carefully controlling the tradeoff between the accuracy and cost of
Value Iteration updates, we achieve an ergodic convergence rate of for the best
choice of parameters on ellipsoidal and Kullback-Leibler -rectangular
uncertainty sets, where and is the number of states and actions,
respectively. Our dependence on the number of states and actions is
significantly better (by a factor of ) than that of pure
Value Iteration algorithms. In numerical experiments on ellipsoidal uncertainty
sets we show that our algorithm is significantly more scalable than
state-of-the-art approaches. Our framework is also the first one to solve
robust MDPs with -rectangular KL uncertainty sets
L'Ă©toffe des dieux. Les consĂ©crations de vĂȘtements dans le monde grec : autour du culte attique d'ArtĂ©mis Brauronia
Publication suite au Colloque international "Agalma ou les figurations de lâinvisible". Approches comparĂ©es. OrganisĂ© par Marcello Carastro (EHESS), Ivonne Manfrini (Haute Ecole dâArt et de Design de GenĂšve) et StĂ©phan Dugast (IRD), Paris, 13 et 14 fĂ©vrier 2012. Actes du colloque Ă paraĂźtre.INHA, 2 rue Vivienne 75002 Paris.In many Greek sanctuaries, worshippers used to dedicate textiles to the deities. Two main kinds of dedications might be found: first, occasional offerings of clothing previously worn, that aim at creating an intimate relationship between the dedicant (mostly women) and the deity ; second, the annual offering, on behalf of a whole city, of a brand-new fabric that was woven especially for this purpose, and was conveyed through a procession to dress the divine statue during public festivals. This paper will analyze the close relationship between the two types of dedications, by studying the case of the attic worship of Artemis in Brauron. Relying mainly on epigraphic testimonies (public inventories of textile offerings), I will try to shed light on the « agalmatic » aspect of such textile offerings. A comparison will thus be drawn with the catholic cult of Virgins, as studied by MarlĂšne Albert Llorca, and in particular with the worship of the Black Virgin of La Daurade in Toulouse, during modern times. By doing so, I will show that the sharp distinction between individual and public offerings, often assumed by ancient Greek historians, should be reconsidered.Lâoffrande de piĂšces de tissu aux divinitĂ©s constitue un acte de piĂ©tĂ© rĂ©pandu dans le monde grec. Par-delĂ la diversitĂ© des formes quâelle peut prendre, on a tendance Ă distinguer deux principaux cas de figure. Dâun cĂŽtĂ©, les consĂ©crations ponctuelles de vĂȘtements effectivement portĂ©s par des individus sont liĂ©es Ă des circonstances particuliĂšres et visent Ă crĂ©er une proximitĂ© entre le dĂ©dicant et la divinitĂ©. De lâautre, la remise par lâensemble de la communautĂ© dâune piĂšce dâĂ©toffe neuve, tissĂ©e Ă cet effet pour ĂȘtre apportĂ©e en procession et vĂȘtir lâeffigie divine, a lieu lors de fĂȘtes impliquant toute la citĂ©. Selon que lâon se situe dans lâun ou lâautre registre, acte de dĂ©votion privĂ© ou rite public, les acteurs, les motivations, la nature des offrandes dĂ©posĂ©es, les temporalitĂ©s diffĂšrent. Câest sur ces points que lâarticle se propose de revenir, en Ă©tudiant le dossier relatif aux vĂȘtements consacrĂ©s dans le sanctuaire dâArtĂ©mis Ă Brauron, en Attique. LâĂ©tude, qui sâappuie principalement sur la documentation Ă©pigraphique, cherche Ă montrer en quoi les offrandes textiles relĂšvent de lâ« agalmatique ». Pour ce faire, une comparaison est Ă©tablie avec les donnĂ©es rassemblĂ©es par MarlĂšne Albert Llorca sur le culte marial Ă lâĂ©poque moderne et alimentĂ©e par lâanalyse des archives relatives au culte de la Vierge Noire de la Daurade, Ă Toulouse. La confrontation sâavĂšre fĂ©conde et permet de considĂ©rer sous un angle neuf les pratiques votives qui ont lieu Ă Brauron. Elle montre notamment que la distinction entre offrandes « publiques » et offrandes « privĂ©es » mĂ©rite dâĂȘtre reconsidĂ©rĂ©e
Hittorff, un architecte Ă l'Ă©cole de la GrĂšce
Jacques-Ignace Hittorff (1792-1867) appears as a figure at once emblematic and singular in XIXth century Europe. That architect and archeologist from the Rhineland got his formation at the Ecole des Beaux-Arts and settled in Paris to exercise his talents as a Hellenist and artist. He contributed to the advances of archeological science by becoming the inventor and theoretician of the monumental polychromy of the Greeks. Reviving the link between antique and modern architecture on new foundations, he promoted a freer reappropriation of the classical tradition and helped to precipitate the end of the reign of neo-classicism then prevailing in Europe. He thus put to advantage his erudite research to conceive edifices that bear the trace of a daring grafting of the antique coloured pattern: this is the case with the Cirque d'Hiver and Saint-Vincent de Paul's church. Still, the relationship between his activities as archeologist and those as architect is not a one-way affair: they entertain a dynamic, complex dialectic relationship. As a matter of fact, his work as historian was for a large part motivated and guided by his desire to justify and make acceptable for the Parisians his own polychromic projects.Jacques-Ignace Hittorff (1792-1867) apparaĂźt comme une figure Ă la fois emblĂ©matique et singuliĂšre dans l'Europe du xixe siĂšcle. Cet architecte et archĂ©ologue originaire de RhĂ©nanie, formĂ© Ă l'Ăcole des Beaux-Arts, s'est installĂ© Ă Paris pour y exercer ses talents d'hellĂ©niste et d'artiste. Il a contribuĂ© aux progrĂšs de la science archĂ©ologique, en se faisant l'inventeur et le thĂ©oricien de la polychromie monumentale des Grecs. Renouant le lien entre l'architecture antique et l'architecture moderne sur des bases neuves, il a promu une rĂ©appropriation plus libre de la tradition classique et a contribuĂ© Ă prĂ©cipiter la fin du rĂšgne du nĂ©o-classicisme, alors dominant en Europe. Il a ainsi mis Ă profit le fruit de ses recherches Ă©rudites pour concevoir des Ă©difices qui portent la trace d'une greffe audacieuse de la bigarrure antique : c'est le cas du Cirque d'Hiver et de l'Ă©glise Saint-Vincent de Paul. Pour autant, le rapport tissĂ© entre ses activitĂ©s d'archĂ©ologue et celles d'architecte n'est pas Ă sens unique : elles entretiennent une relation dialectique dynamique et complexe. En effet, son travail d'historien a Ă©tĂ© pour une bonne part motivĂ© et guidĂ© par un dĂ©sir de justifier et de faire accepter auprĂšs des Parisiens ses propres projets polychromes
The Best Decisions Are Not the Best Advice: Making Adherence-Aware Recommendations
Many high-stake decisions follow an expert-in-loop structure in that a human
operator receives recommendations from an algorithm but is the ultimate
decision maker. Hence, the algorithm's recommendation may differ from the
actual decision implemented in practice. However, most algorithmic
recommendations are obtained by solving an optimization problem that assumes
recommendations will be perfectly implemented. We propose an adherence-aware
optimization framework to capture the dichotomy between the recommended and the
implemented policy and analyze the impact of partial adherence on the optimal
recommendation. We show that overlooking the partial adherence phenomenon, as
is currently being done by most recommendation engines, can lead to arbitrarily
severe performance deterioration, compared with both the current human baseline
performance and what is expected by the recommendation algorithm. Our framework
also provides useful tools to analyze the structure and to compute optimal
recommendation policies that are naturally immune against such human
deviations, and are guaranteed to improve upon the baseline policy
On the convex formulations of robust Markov decision processes
Robust Markov decision processes (MDPs) are used for applications of dynamic
optimization in uncertain environments and have been studied extensively. Many
of the main properties and algorithms of MDPs, such as value iteration and
policy iteration, extend directly to RMDPs. Surprisingly, there is no known
analog of the MDP convex optimization formulation for solving RMDPs. This work
describes the first convex optimization formulation of RMDPs under the
classical sa-rectangularity and s-rectangularity assumptions. By using entropic
regularization and exponential change of variables, we derive a convex
formulation with a number of variables and constraints polynomial in the number
of states and actions, but with large coefficients in the constraints. We
further simplify the formulation for RMDPs with polyhedral, ellipsoidal, or
entropy-based uncertainty sets, showing that, in these cases, RMDPs can be
reformulated as conic programs based on exponential cones, quadratic cones, and
non-negative orthants. Our work opens a new research direction for RMDPs and
can serve as a first step toward obtaining a tractable convex formulation of
RMDPs
Charlotte Ribeyrol, « ĂtrangetĂ©, passion, couleur ». LâhellĂ©nisme de Swinburne, Pater et Symonds (1865-1880)
Lâouvrage, issu dâune thĂšse de doctorat en littĂ©rature britannique, invite Ă dĂ©couvrir lâhellĂ©nisme de trois auteurs de lâAngleterre victorienne, Swinburne, Pater et Symonds, dont lâĆuvre constitue une Ă©tape majeure dans le renouvellement du rapport Ă lâAntiquitĂ©, entre la tradition nĂ©o-classique et les lectures des Modernistes. Câest le moment oĂč la GrĂšce, de mieux en mieux connue grĂące au progrĂšs de lâarchĂ©ologie, tend Ă supplanter Rome et Ă sâaffirmer par rapport au modĂšle de rĂ©fĂ©rence hĂ©b..
Florence Gherchanoc, Lâoikos en fĂȘte. CĂ©lĂ©brations familiales et sociabilitĂ© en GrĂšce ancienne
La sphĂšre domestique est sans aucun doute lâun des lieux privilĂ©giĂ©s pour observer et analyser lâimbrication du « public » et du « privé » dans la citĂ© grecque, notamment en matiĂšre de pratiques religieuses : lâouvrage de Florence Gherchanoc (F.G.) le montre bien. Lâoikos y est apprĂ©hendĂ© sous lâangle des « fĂȘtes et cĂ©lĂ©brations » qui rythment la vie de la maisonnĂ©e, principalement aux Ă©poques archaĂŻque et classique. Lâobjectif affichĂ© est de faire converger, dâune part, les Ă©tudes rĂ©centes s..
Le musée Saint-Raymond, musée des Antiques de Toulouse, et ses portraits romains
En guise de prĂ©sentation Lâhistoire de la rĂ©ception de lâAntiquitĂ© se nourrit de celle de lâaccueil rĂ©servĂ© aux Ćuvres antiques, qui contribuent tout autant que les textes Ă la connaissance des civilisations passĂ©es. Au cours du xixe siĂšcle, la « naissance » de lâarchĂ©ologie moderne modifie profondĂ©ment le regard portĂ© sur les objets antiques, amorçant une Ă©volution du statut qui leur est dĂ©volu. La recherche du « bel objet », Ćuvre dâart Ă©levĂ©e au rang de modĂšle indĂ©passable, qui suscite adm..
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