A Lower Bound for Randomized Searching on m Rays

  • Sven Schuierer
Part of the Lecture Notes in Computer Science book series (LNCS, volume 2598)


We consider the problem of on-line searching on m rays. A point robot is assumed to stand at the origin of m concurrent rays one of which contains a goal g that the point robot has to find. Neither the ray containing g nor the distance to g are known to the robot. The only way the robot can detect g is by reaching its location. We use the competitive ratio as a measure of the performance of a search strategy, that is, the worst case ratio of the total distance D R traveled by the robot to find g to the distance D from the origin to g. We present a new proof of a tight lower bound of the competitive ratio for randomized strategies to search on m rays. Our proof allows us to obtain a lower bound on the optimal competitive ratio for a fixed m even if the distance of the goal to the origin is bounded from above. Finally, we show that the optimal competitive ratio converges to 1+2(e α - 1)/α2 m∼1+2·1.544m, for large m where á minimizes the function (e x-1)/x 2.


Step Length Competitive Ratio Simple Polygon Goal Position Hiding Strategy 
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© Springer-Verlag Berlin Heidelberg 2003

Authors and Affiliations

  • Sven Schuierer
    • 1
  1. 1.Novartis Pharma AGBaselSwitzerland

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