Letteratura scientifica selezionata sul tema "Algorothm"

In article discusses issues for solving optimization problems based on the use of genetic algorithms. To date, the genetic use algorithm for solving various problems. Which includes the shortest path search, approximation, data filtering and others. In particular, data is being examined regarding the use of a genetic algorithm to solve problems of optimizing the modes of electric power systems. Imagine an algorithm for developing the development of mathematical models, which includes developing the structure of the chromosome, creating a started population, creating a directing force for the population, etc. As well as the presentation, the selected structure should take into account all the features and limitations imposed on the desired solution, as well as the fact that the implementation of crossоver and mutation algorithms directly depends on its choice. To solve optimization problems, a block diagram of the genetic algorithm is given.

The 2-groups of coclass 1 are widely known and James (in 1975) looked at the 2-groups of coclass 2. Development of the p-group generation algorithm implemented by O'Brien at ANU enabled group presentations to be provided for the 2-groups of coclass 3 by Newman and O'Brien for groups of order up to 223. Newman and O'Brien (in 1999) conjectured the number of descendants of 2n for all n. They introduced the concept of a family, with each family related to a different pro-p-group and the concept of a sporadic p-group, a p-group external to any family. They found 1782 sporadic 2-groups with order at most 214. The 70 families of 2-groups of coclass 3 can be further split according to their period, a measure of the repetitive structure of the families. Newman and O'Brien conjectured that these families had periods of 1, 2 or 4. This thesis examines the 2-groups of coclass 3 contained in families with period 1 and shows that the number of descendants conjectured by Newman and O'Brien is correct. Furthermore the presentation of all groups contained in period 1 families is provided and shown to be correct.

L'autonomie est l'une des préoccupations majeures lors du développement de missions spatiales que l'objectif soit scientifique (exploration interplanétaire, observations, etc) ou commercial (service en orbite). Pour le rendez-vous spatial, cette autonomie dépend de la capacité embarquée de contrôle du mouvement relatif entre deux véhicules spatiaux. Dans le contexte du service aux satellites (dépannage, remplissage additionnel d'ergols, correction d'orbite, désorbitation en fin de vie, etc), la faisabilité de telles missions est aussi fortement liée à la capacité des algorithmes de guidage et contrôle à prendre en compte l'ensemble des contraintes opérationnelles (par exemple, saturation des propulseurs ou restrictions sur le positionnement relatif entre les véhicules) tout en maximisant la durée de vie du véhicule (minimisation de la consommation d'ergols). La littérature montre que ce problème a été étudié intensément depuis le début des années 2000. Les algorithmes proposés ne sont pas tout à fait satisfaisants. Quelques approches, par exemple, dégradent les contraintes afin de pouvoir fonder l'algorithme de contrôle sur un problème d'optimisation efficace. D'autres méthodes, si elles prennent en compte l'ensemble du problème, se montrent trop lourdes pour être embarquées sur de véritables calculateurs existants dans les vaisseaux spatiaux. Le principal objectif de cette thèse est le développement de nouveaux algorithmes efficaces et validés pour le guidage et le contrôle impulsif des engins spatiaux dans le contexte des phases dites de "hovering" du rendez-vous orbital, i.e. les étapes dans lesquelles un vaisseau secondaire doit maintenir sa position à l'intérieur d'une zone délimitée de l'espace relativement à un autre vaisseau principal. La première contribution présentée dans ce manuscrit utilise une nouvelle formulation mathématique des contraintes d'espace pour le mouvement relatif entre vaisseaux spatiaux pour la conception d'algorithmes de contrôle ayant un traitement calculatoire plus efficace comparativement aux approches traditionnelles. La deuxième et principale contribution est une stratégie de contrôle prédictif qui assure la convergence des trajectoires relatives vers la zone de "hovering", même en présence de perturbations ou de saturation des actionneurs. [...]<br>Autonomy is one of the major concerns during the planning of a space mission, whether its objective is scientific (interplanetary exploration, observations, etc.) or commercial (service in orbit). For space rendezvous, this autonomy depends on the on-board capacity of controlling the relative movement between two spacecraft. In the context of satellite servicing (troubleshooting, propellant refueling, orbit correction, end-of-life deorbit, etc.), the feasibility of such missions is also strongly linked to the ability of the guidance and control algorithms to account for all operational constraints (for example, thruster saturation or restrictions on the relative positioning between the vehicles) while maximizing the life of the vehicle (minimizing propellant consumption). The literature shows that this problem has been intensively studied since the early 2000s. However, the proposed algorithms are not entirely satisfactory. Some approaches, for example, degrade the constraints in order to be able to base the control algorithm on an efficient optimization problem. Other methods accounting for the whole set of constraints of the problem are too cumbersome to be embedded on real computers existing in the spaceships. The main object of this thesis is the development of new efficient and validated algorithms for the impulsive guidance and control of spacecraft in the context of the so-called "hovering" phases of the orbital rendezvous, i.e. the stages in which a secondary vessel must maintain its position within a bounded area of space relatively to another main vessel. The first contribution presented in this manuscript uses a new mathematical formulation of the space constraints for the relative motion between spacecraft for the design of control algorithms with more efficient computational processing compared to traditional approaches. The second and main contribution is a predictive control strategy that has been formally demonstrated to ensure the convergence of relative trajectories towards the "hovering" zone, even in the presence of disturbances or saturation of the actuators.[...]