Gerhard Trippen

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We study the problem of exploring an unknown, strongly connected directed graph. Starting at some node of the graph, we must visit every edge and every node at least once. The goal is to minimize the number of edge traversals. It is known that the competitive ratio of online algorithms for this problem depends on the deficiency d of the graph, which is the(More)
How efficiently can we search an unknown environment for a goal in unknown position? How much would it help if the environment were known? We answer these questions for simple polygons and for general graphs, by providing online search strategies that are as good as the best offline search algorithms, up to a constant factor. For other settings we prove(More)
We consider the problem of a searcher that looks, for example, for a lost flashlight in a dusty environment. The search agent finds the flashlight as soon as it crosses the ray emanating from the flashlight, and in order to pick it up, the searcher has to move to the origin of the light beam. First, we give a search strategy for a special case of the ray(More)
The problem of localization, i.e. of a robot finding its pcrsition on a map, is an important task for autonomous mobile robots. It has applications in numerous areas of robotics ranging from aerial photography to autonomous vehicle exploration. In this paper we present a new strategy for a robot to find its position on a map where the map is represented as(More)
We define simple-regular expressions and languages. Simple-regular languages provide a necessary condition for a language to be outfix-free. We design algorithms that compute simple-regular languages from finite-state automata. Furthermore, we investigate the complexity blowup from a given finite-state automaton to its simple-regular language automaton and(More)
We consider the problem of searching for a goal in an unknown environment, which may be a graph or a polygonal environment. The search ratio is the worst-case ratio before the goal is found while moving along some search path, over the shortest path from the start point to the goal, minimized over all search paths. We investigate the problem of finding good(More)