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Huber-energy measure quantization
No full textInternational audienceWe describe a measure quantization procedure i.e., an algorithm which finds the best approximation of a target probability law (and more generally signed finite variation measure) by a sum of Q Dirac masses (Q being the quantization parameter). The procedure is implemented by minimizing the statistical distance between the original measure and its quantized version; the distance is built from a negative definite kernel and, if necessary, can be computed on the fly and feed to a stochastic optimization algorithm (such as SGD, Adam, ...). We investigate theoretically the fundamental questions of existence of the optimal measure quantizer and identify what are the required kernel properties that guarantee suitable behavior. We test the procedure, called HEMQ, on several databases: multi-dimensional Gaussian mixtures, Wiener space cubature, Italian wine cultivars and the MNIST image database. The results indicate that the HEMQ algorithm is robust and versatile and, for the class of Huber-energy kernels, it matches the expected intuitive behavior
Quantitative conditions for right-handedness
No full textInternational audienceWe give a numerical condition for right-handedness of a dynamically convex Reeb flow on S^3. Our condition is stated in terms of an asymptotic ratio between the amount of rotation of the linearised flow and the linking number of trajectories with a periodic orbit that spans a disk-like global surface of section. As an application, we find an explicit constant δ * < 0.7225 such that if a Riemannian metric on the 2-sphere is δ-pinched with δ > δ * , then its geodesic flow lifts to a right-handed flow on S^3. In particular, all finite collections of periodic orbits of such a geodesic flow bind open books whose pages are global surfaces of section
Direct-search methods in the year 2025: Theoretical guarantees and algorithmic paradigms
No full textInternational audienceOptimizing a function without using derivatives is a challenging paradigm, that precludes from using classical algorithms from nonlinear optimization, and may thus seem intractable other than by using heuristics. Nevertheless, the field of derivative-free optimization has succeeded in producing algorithms that do not rely on derivatives and yet are endowed with convergence guarantees. One class of such methods, called direct-search methods, is particularly popular thanks to its simplicity of implementation, even though its theoretical underpinnings are not always easy to grasp.In this work, we survey contemporary direct-search algorithms from a theoretical viewpoint, with the aim of highlighting the key theoretical features of these methods. We provide a basic introduction to the main classes of direct-search methods, including line-search techniques that have received little attention in earlier surveys. We also put a particular emphasis on probabilistic direct-search techniques and their application to noisy problems, a topic that has undergone significant algorithmic development in recent years. Finally, we complement existing surveys by reviewing the main theoretical advances for solving constrained and multiobjective optimization using direct-search algorithms
Mobiliser le secteur assurantiel européen dans la lutte contre le réchauffement climatique
No full textClimate change is one of the greatest challenges of the 21st century, requiring a profound transformation of economies and massive investment programs. Institutional investors—particularly European insurers through life insurance savings—can play a key role in financing the low-carbon transition. This thesis explores the levers that could be used to mobilize these resources while preserving the financial stability of the sector.The first chapter highlights the limitations of investment strategies based on carbon footprint. While effective in reducing portfolio emissions, these approaches introduce sectoral and geographical biases, notably underinvesting in the energy sector and emerging markets. It is therefore necessary to develop strategies that incorporate both the dynamics of decarbonization and the green investments made by issuers.The second chapter proposes integrating climate risk into the Solvency Capital Requirement (SCR) under Pillar 1 of Solvency II. Such a reform would significantly reduce solvency ratios, potentially exposing 10% of insurers to a capital shortfall. This systemic risk could undermine policyholder confidence. However, it could also serve as a powerful green financing lever: by exempting green bonds from the climate SCR, regulators could incentivize insurers to support the energy transition.Finally, the third chapter examines the valuation of life insurance contracts in the face of climate risk. Introducing a climate SCR reduces insurers’ ability to invest in risky assets, thereby lowering the value of profit-sharing options. To preserve the appeal of these products, the thesis proposes a green, compartmentalized life insurance contract invested exclusively in transition-aligned assets. This structure would help restore value for policyholders while channeling long-term savings toward sustainable investments.La lutte contre le réchauffement climatique constitue un défi majeur du XXIe siècle, nécessitant une transformation profonde des économies et des investissements massifs. Les investisseurs institutionnels, et en particulier les assureurs européens via l’assurance-vie, peuvent jouer un rôle clé dans le financement de la transition bas carbone. Cette thèse explore les leviers permettant de mobiliser ces ressources tout en assurant la stabilité du secteur. Le premier chapitre met en évidence les limites des stratégies d’investissement fondées sur l’empreinte carbone. Bien qu’efficaces pour réduire les émissions apparentes, ces approches induisent des biais sectoriels et géographiques, notamment un sous-investissement dans l’énergie et les pays émergents. Il est donc nécessaire de développer des stratégies intégrant la dynamique de décarbonation et les investissements verts des émetteurs. Le deuxième chapitre propose d’intégrer le risque climatique dans le calcul du capital réglementaire (SCR) de Solvabilité II. Une telle réforme réduirait significativement les ratios de solvabilité, exposant 10% des assureurs à un déficit de fonds propres. Ce risque systémique pourrait fragiliser la confiance des épargnants. Toutefois, il pourrait aussi devenir un levier de financement vert : en exonérant les obligations vertes du SCR climatique, le régulateur inciterait les assureurs à financer la transition énergétique. Enfin, le troisième chapitre s’intéresse à la valorisation des contrats d’assurance-vie face au risque climatique. L’introduction d’un SCR climatique réduit la capacité des assureurs à investir dans des actifs risqués, diminuant la valeur des options de participation aux bénéfices. Pour préserver l’attractivité de ces produits, la thèse propose un contrat d’assurance-vie vert compartimenté, investi exclusivement dans des actifs alignés sur la transition. Ce contrat permettrait de restaurer la valeur pour les assurés tout en orientant l’épargne longue vers des investissements durables
Voici venu le temps de l'instabilité hégémonique
No full texthttps://geopoweb.fr/?VOICI-VENU-LE-TEMPS-DE-L-INSTABILITE-HEGEMONIQUE-Jean-Marc-SIROENAprès des années d’ambiguïté, la question semble tranchée : la politique extérieure des Etats-Unis sera fondée sur un unilatéralisme mâtiné d’isolationnisme. » Dans ce bel article, Jean Marc Siroën (1) met en perspective la phase de création d’une jurisprudence commerciale internationale (un droit certes imparfait mais assurant une certaine visibilité) avec la doctrine commerciale historique des Etats-Unis (reposant souvent sur un mercantilisme chronique). Le trumpisme introduit un point de rupture significatif : le principe de « stabilité hégémonique » avec une certaine bienveillance et relevant d’une certaine maturité est désormais balayé par un mercantilisme désordonné, pur et dur... Nul doute que l’incertitude ouvre les perspectives de stratégies opportunistes d’autres puissances..
Finding a better job: The geography of socio-professional mobility during working life
No full textInternational audienceWhat determines the chances of moving up or down to better or worse jobs? We examine how local labor markets influence individuals’ socio-professional mobility throughout their working lives, focusing on large promotions and demotions. Using an empirical strategy that accounts for spatial sorting bias, applied to a sample of approximately 350,000 workers in France between 2009 and 2015, we find that job density, local human capital, and labor market size significantly increase the likelihood of being promoted to a higher socio-professional status. The effect of local factors is stronger for external promotions (outside the firm) than for internal ones. Moreover, experience accumulated in the most densely populated and educated areas continues to enhance promotion prospects, even after relocating to less dense or educated areas. This dynamic effect of promotion explains around 16% of the wage premium associated with experience in dense areas. Finally, we show that agglomerations effects on promotion are driven more by human capital externalities and proximity to other dense markets than by pure urbanization or scale effects
Derrière Temu, le succès d’un modèle Made in China
No full textLes succès rencontrés par Temu s’inscrivent dans une politique plus générale du gouvernement chinois pour stimuler les exportations. L’e-commerçant a ainsi pu profiter à de multiples infrastructures développées par l’État chinois.Alors que les tensions commerciales se multiplient entre la Chine, les États-Unis et l’Union européenne, le pavillon chinois va-t-il devenir un handicap pour la plateforme ? ou l’agilité de Temu l’aidera-t-elle à passer ce moment