Browsing by Subject "Heuristic programming."

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Open Access
A collaborative system for providing routes between locations
(2008) Uluğ, Kerem Ali
Many systems, such as in-car GPS devices and airline company web sites, provide route information between locations. Although such systems are used widely and can provide route information successfully, users of these systems cannot contribute to the data entry process. In these systems, data is entered by the administrators and these systems cannot take advantage of the route expertise of their users. In this work, we present a collaborative system, which provides routes between locations upon user queries. The data in the system is entered by the users of the system. We present a model which is containing locations, links between locations and relationships between locations (containment, neighborhood and intersection) in order to store the data. For the route finding purpose, we present a customized version of the A* search algorithm. This customized version, named A*CD (A* for Collaborative Data), uses heuristics for estimating the cost remaining to the target location while processing the nodes. A*CD can also provide alternative routes, exclude certain link types in the searches according to user preferences and handle the problems associated with multiple stop transportation lines. As the cost models, we use duration and financial cost. We also present the intuitive connections concept. Even if a route does not exist between the selected locations, the system can provide a route with missing links. The gap(s) between the disconnected locations are filled by the help of the relationships between locations. In order to evaluate the performance of the A*CD algorithm, we present automated tests. These tests show that the costs of the routes that are provided by the A*CD algorithm are close to the actual shortest routes. In order to demonstrate the intuitive connections concept, we also present manual test queries.
Open Access
Generating short-term observation schedules for space mission projects
(1997) Kılıç, Kemal
Space mission scheduling (SMS) has been an important research area for several years. The basic features of the space mission projects are the high investment and operational costs, and limited resource availability. Therefore, it is very important to justify the high investment on the space mission projects by generating good schedules. In this thesis, we have proposed several new solution algorithms for generating short term observation schedules of space mission projects and test their efficiencies on a good representative of SMS problem; Hubble Space Telescope (HST) scheduling problem. HST is an exceptional space observatory at low earth orbit among the others that are used for space exposures. The main features of generating short-term observations of HST are state dependent set up times, user specified due dates, priorities and the visibility windows assigned to the candidate observations. The objective of HST scheduling is to maximize the scientific return. We have proposed four new algorithms. The first one is a new dispatch rule that considers the basic features of the problem domain while scheduling the observations. The second one is a filtered beam search algorithm. We have introduced a new concept of childwidth, which is a parameter that restricts the number of beams that generates from the same parent. The third one is a Greedy Randomized Adaptive Search Procedure (GRASP) that needs to be tailored to be applicable to the problem domain. Finally, we proposed a simulated annealing algorithm with a new introduced concept of mutation. We have tested the relative performances of the proposed algorithms, as well as the nearest neighbor algorithm, both in objective function value and computational time aspects by utilizing a 2^ full-factorial experimental design.
Open Access
A polyhedral approach to delivery man problem
(1992) Keskinocak, Pınar
In this thesis we discuss some polyhedral approaches to the Delivery Man Problem(DMP),which is a special case of the Traveling .Scvlesman Problem(TSP). First, we look at two formulations of the problem and describe a combinatorial solution procedure for the linear programming relaxation.Then we give some valid inequalities and discuss a Lagrangean Relaxation procedure and a cutting plane procedure. Finally, we propose heuristics for tree graphs and general graphs and give computational results.