The power of a pebble: exploring and mapping directed graphs
STOC '98 Proceedings of the thirtieth annual ACM symposium on Theory of computing
On agent-based software engineering
Artificial Intelligence
Exploring unknown undirected graphs
Journal of Algorithms
The freeze-tag problem: how to wake up a swarm of robots
SODA '02 Proceedings of the thirteenth annual ACM-SIAM symposium on Discrete algorithms
Capture of an intruder by mobile agents
Proceedings of the fourteenth annual ACM symposium on Parallel algorithms and architectures
Searching for a black hole in arbitrary networks: optimal mobile agent protocols
Proceedings of the twenty-first annual symposium on Principles of distributed computing
One Pebble Does Not Suffice to Search Plane Labyrinths
FCT '81 Proceedings of the 1981 International FCT-Conference on Fundamentals of Computation Theory
Protecting Mobile Agents Against Malicious Hosts
Mobile Agents and Security
Graph exploration by a finite automaton
Theoretical Computer Science - Mathematical foundations of computer science 2004
Networks
Mobile Search for a Black Hole in an Anonymous Ring
Algorithmica
Tree exploration with logarithmic memory
SODA '07 Proceedings of the eighteenth annual ACM-SIAM symposium on Discrete algorithms
Label-guided graph exploration by a finite automaton
ACM Transactions on Algorithms (TALG)
SFCS '90 Proceedings of the 31st Annual Symposium on Foundations of Computer Science
The power of team exploration: two robots can learn unlabeled directed graphs
SFCS '94 Proceedings of the 35th Annual Symposium on Foundations of Computer Science
Impact of memory size on graph exploration capability
Discrete Applied Mathematics
Information and Computation
Host revocation authority: a way of protecting mobile agents from malicious hosts
ICWE'03 Proceedings of the 2003 international conference on Web engineering
Asynchronous deterministic rendezvous in graphs
MFCS'05 Proceedings of the 30th international conference on Mathematical Foundations of Computer Science
Searching for a black hole in tree networks
OPODIS'04 Proceedings of the 8th international conference on Principles of Distributed Systems
Hardness and approximation results for black hole search in arbitrary graphs
SIROCCO'05 Proceedings of the 12th international conference on Structural Information and Communication Complexity
Research note: Security issues related to mobile code and agent-based systems
Computer Communications
IEEE Communications Magazine
Synchronization Helps Robots to Detect Black Holes in Directed Graphs
OPODIS '09 Proceedings of the 13th International Conference on Principles of Distributed Systems
Rendezvous of mobile agents in directed graphs
DISC'10 Proceedings of the 24th international conference on Distributed computing
Time optimal algorithms for black hole search in rings
COCOA'10 Proceedings of the 4th international conference on Combinatorial optimization and applications - Volume Part II
Synchronous black hole search in directed graphs
Theoretical Computer Science
Tight bounds for scattered black hole search in a ring
SIROCCO'11 Proceedings of the 18th international conference on Structural information and communication complexity
Improving the optimal bounds for black hole search in rings
SIROCCO'11 Proceedings of the 18th international conference on Structural information and communication complexity
Black hole search with finite automata scattered in a synchronous torus
DISC'11 Proceedings of the 25th international conference on Distributed computing
Periodic data retrieval problem in rings containing a malicious host
SIROCCO'10 Proceedings of the 17th international conference on Structural Information and Communication Complexity
Asynchronous exploration of an unknown anonymous dangerous graph with o(1) pebbles
SIROCCO'12 Proceedings of the 19th international conference on Structural Information and Communication Complexity
Fault-Tolerant exploration of an unknown dangerous graph by scattered agents
SSS'12 Proceedings of the 14th international conference on Stabilization, Safety, and Security of Distributed Systems
Exploring an unknown dangerous graph using tokens
Theoretical Computer Science
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We consider the problem of cooperative network exploration by agents under the assumption that there is a harmful host present in the network that destroys the incoming agents without outside trace – the so-called black hole search problem. Many variants of this problem have been studied, with various assumptions about the timing, agents' knowledge about the topology, means of inter-agent communication, amount of writable memory in vertices, and other parameters. However, all this research considered undirected graphs only, and relied to some extent on the ability of an agent to mark an edge as safe immediately after having traversed it. In this paper we study directed graphs where this technique does not apply, and show that the consequence is an exponential gap: While in undirected graphs Δ+1 agents are always sufficient, in the directed case at least 2Δ agents are needed in the worst case, where Δ is in-degree of the black hole. This lower bound holds also in the case of synchronous agents. Furthermore, we ask the question What structural information is sufficient to close this gap? and show that in planar graphs with a planar embedding known to the agents, 2Δ+1 agents are sufficient, and 2Δ agents are necessary.