In this thesis we study two optimization fields. In a first part, we study the use of evolutionary algorithms for solving derivative-free optimization problems in continuous space. In a second part we are interested in multistage optimization. In that case, we have to make decisions in a discrete environment with finite horizon and a large number of states. In this part we use in particular Monte-Carlo Tree Search algorithms. In the first part, we work on evolutionary algorithms in a parallel context, when a large number of processors are available. We start by presenting some state of the art evolutionary algorithms, and then, show that these algorithms are not well designed for parallel optimization. Because these algorithms are population based, they should be we well suitable for parallelization, but the experiments show that the results are far from the theoretical bounds. In order to solve this discrepancy, we propose some rules (such as a new selection ratio or a faster decrease of the step-size) to improve the evolutionary algorithms. Experiments are done on some evolutionary algorithms and show that these algorithms reach the theoretical speedup with the help of these new rules.Concerning the work on multistage optimization, we start by presenting some of the state of the art algorithms (Min-Max, Alpha-Beta, Monte-Carlo Tree Search, Nested Monte-Carlo). After that, we show the generality of the Monte-Carlo Tree Search algorithm by successfully applying it to the game of Havannah. The application has been a real success, because today, every Havannah program uses Monte-Carlo Tree Search algorithms instead of the classical Alpha-Beta. Next, we study more precisely the Monte-Carlo part of the Monte-Carlo Tree Search algorithm. 3 generic rules are proposed in order to improve this Monte-Carlo policy. Experiments are done in order to show the efficiency of these rules.

Cette thèse se situe dans le contexte de l'optimisation. Deux grandes parties s'en dégagent ; la première concerne l'utilisation d'algorithmes évolutionnaires pour résoudre des problèmes d'optimisation continue et sans dérivées. La seconde partie concerne l'optimisation de séquences de décisions dans un environnement discret et à horizon fini en utilisant des méthodes de type Monte-Carlo Tree Search. Dans le cadre de l'optimisation évolutionnaire, nous nous intéressons particulièrement au cadre parallèle à grand nombre d'unités de calcul. Après avoir présenté les algorithmes de référence du domaine, nous montrons que ces algorithmes, sous leur forme classique, ne sont pas adaptés à ce cadre parallèle et sont loin d'atteindre les vitesses de convergence théoriques. Nous proposons donc ensuite différentes règles (comme la modification du taux de sélection des individus ainsi que la décroissance plus rapide du pas) afin de corriger et améliorer ces algorithmes. Nous faisons un comparatif empirique de ces règles appliquées à certains algorithmes. Dans le cadre de l'optimisation de séquences de décisions, nous présentons d'abord les algorithmes de référence dans ce domaine (Min-Max, Alpha-Beta, Monte-carlo Tree Search, Nested Monte-Carlo). Nous montrons ensuite la généricité de l'algorithme Monte-Carlo Tree Search en l'appliquant avec succès au jeu de Havannah. Cette application a été un réel succès puisqu'aujourd'hui les meilleurs joueurs artificiels au jeu de Havannah utilisent cet algorithme et non plus des algorithmes de type Min-Max ou Alpha-Beta. Ensuite, nous nous sommes particulièrement intéressés à l'amélioration de la politique Monte-Carlo de ces algorithmes. Nous proposons trois améliorations, chacune étant générique. Des expériences sont faites pour mesurer l'impact de ces améliorations, ainsi que la généricité de l'une d'entre elles. Nous montrons à travers ces expériences que les résultats sont positifs. / In this thesis we study two optimization fields. In a first part, we study the use of evolutionary algorithms for solving derivative-free optimization problems in continuous space. In a second part we are interested in multistage optimization. In that case, we have to make decisions in a discrete environment with finite horizon and a large number of states. In this part we use in particular Monte-Carlo Tree Search algorithms. In the first part, we work on evolutionary algorithms in a parallel context, when a large number of processors are available. We start by presenting some state of the art evolutionary algorithms, and then, show that these algorithms are not well designed for parallel optimization. Because these algorithms are population based, they should be we well suitable for parallelization, but the experiments show that the results are far from the theoretical bounds. In order to solve this discrepancy, we propose some rules (such as a new selection ratio or a faster decrease of the step-size) to improve the evolutionary algorithms. Experiments are done on some evolutionary algorithms and show that these algorithms reach the theoretical speedup with the help of these new rules.Concerning the work on multistage optimization, we start by presenting some of the state of the art algorithms (Min-Max, Alpha-Beta, Monte-Carlo Tree Search, Nested Monte-Carlo). After that, we show the generality of the Monte-Carlo Tree Search algorithm by successfully applying it to the game of Havannah. The application has been a real success, because today, every Havannah program uses Monte-Carlo Tree Search algorithms instead of the classical Alpha-Beta. Next, we study more precisely the Monte-Carlo part of the Monte-Carlo Tree Search algorithm. 3 generic rules are proposed in order to improve this Monte-Carlo policy. Experiments are done in order to show the efficiency of these rules.