Abstract

Let A be any fixed cut-off restart algorithm running in parallel on multiple processors. If the algorithm is only allowed to run for up to time D, then it is no longer guaranteed that a result can be found. In this case, the probability of finding a solution within the time D becomes a measure for the quality of the algorithm. In this paper we address this issue and provide upper and lower bounds for the probability of A finding a solution before a deadline passes under varying assumptions. We also show that the optimal restart times for a fixed cut-off algorithm running in parallel is identical for the optimal restart times for the algorithm running on a single processor. Finally, we conclude that the odds of finding a solution scale superlinearly in the number of processors.

Highlights

  • Restart strategies are commonly used in probabilistic algorithms

  • We show that the optimal restart time regarding completion probability in the case of a fixed cut-off algorithm running on a single processor is optimal for the algorithm running in parallel on multiple processors

  • The optimal restart time regarding completion probability for a fixed-cutoff strategy running on a single processor is identical to the optimal restart time for a fixed-cutoff strategy running on multiple processors

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Summary

Introduction

Restart strategies are commonly used in probabilistic algorithms. If the current computation takes too long, the algorithm is started over with a different random seed. Deciding when to restart is an important task in designing an algorithm and several strategies are known. Luby et al introduced the fixed cut-off strategy . .) in [1] This means after t steps the algorithm is restarted. They showP ed that this strategy is optimal for a certain value of t.

FðtÞ ðt
À FðtkÞ
Notation
FðtÞÞkð1 À
Fðt0ÞÞ2k0
Optimal Restart Time
À Fðtn0 Þ 1 À Fðtm0 Þ
À FðtÞ ð1 À Fðt0ÞÞ
Discussion
FðtÞÞkð2iÀ 1Þð1 À
Conclusion
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