Multirobot tree and graph exploration

Peter Brass, Flavio Cabrera-Mora, Andrea Gasparri, Jizhong Xiao

Research output: Contribution to journalArticlepeer-review

87 Scopus citations


In this paper, we present an algorithm for the exploration of an unknown graph by multiple robots, which is never worse than depth-first search with a single robot. On trees, we prove that the algorithm is optimal for two robots. For k robots, the algorithm has an optimal dependence on the size of the tree but not on its radius. We believe that the algorithm performs well on any tree, and this is substantiated by simulations. For trees with e edges and radius r, the exploration time is less than 2e/k + (1 + (k/r))k-1 (2/k!)r k-1 = (2e/k) + O((k + r)k-1 ) (for r > k, = (2e/k) + 2rk-1 ), thereby improving a recent method with time O((e/log k) + r) [2], and almost reaching the lower bound max((2e/k), 2r). The model underlying undirected-graph exploration is a set of rooms connected by opaque passages; thus, the algorithm is appropriate for scenarios like indoor navigation or cave exploration. In this framework, communication can be realized by bookkeeping devices being dropped by the robots at explored vertices, the states of which are read and changed by further visiting robots. Simulations have been performed in both tree and graph explorations to corroborate the mathematical results.

Original languageEnglish (US)
Article number5739538
Pages (from-to)707-717
Number of pages11
JournalIEEE Transactions on Robotics
Issue number4
StatePublished - Aug 2011

All Science Journal Classification (ASJC) codes

  • Control and Systems Engineering
  • Computer Science Applications
  • Electrical and Electronic Engineering


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