Hislop, Andrew David (1992) Parallel algorithms for digital map path optimisation. University of Southampton, Doctoral Thesis.
Abstract
Working out the best route for a land vehicle to take from its current position to a certain destination can be done relatively quickly and easily by a human, given a map of the area. However, if the map is large and complex, and there are many different constraints on the route taken, then it should be faster to find the optimal route using a computer. Moreover, if the process can be distributed to run on several computers in parallel, the results will be obtained even more quickly. This thesis describes an investigation into finding fast and efficient implementations of parallel algorithms to solve the problem, given a digital map of the area. The target architecture is of the distributed memory MIMD variety and for the particular implementation described in this thesis, a transputer array was used. Firstly, a study of sequential optimum path-finding algorithms is given. Out of the four main algorithms: dynamic programming, Dijkstra's algorithm, d'Esopo's algorithm and branch-and-bound, d'Esopo's algorithm is verified by experiment to be the fastest. The results of distributing Yen's algorithm, a version of dynamic programming, and of distributing d'Esopo's algorithm, are then given. Parallel Yen is found to be fast and have an almost linear improvement in performance with the number of transputers used. However, its performance deteriorates rapidly as the map size is increased. Three different parallel versions of d'Esopo's algorithm are described. Although each is found to have high communication overheads, and to be slower than parallel Yen for the relatively small map sizes used, it is shown that the performances of the second and third parallel d'Esopo programs improve relative to Yen's as the map size is increased. Finally, it is shown how one of these parallel d'Esopo algorithms would be suitable for implementing in a distributed architecture vehicle guidance system.
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