From Simplicity to Complexity Based on Consensus: A Case Study

Distributed consensus has been intensively studied in recent years as a means to mitigate state differences among dynamic nodes on a graph. It has been successfully employed in various applications, e.g., formation control of multi-robots, load balancing, clock synchronization. However, almost all existing applications cast an impression of consensus as a simple process to iteratively reach agreement, without any clue on possibility to generate advanced complexity, say shortest path planning, which has been proved to be NP-hard. Counter-intuitively, we show for the first time that the complexity of shortest path planning can emerge from a perturbed version of min-consensus protocol, which as a case study may shed lights to researchers in the field of distributed control to re-think the nature of complexity and the distance between control and intelligence. Besides, we rigorously prove the convergence of graph dynamics and its equivalence to shortest path solutions. An illustrative simulation on a small scale graph is provided to show the convergence of the biased min-consensus dynamics to shortest path solution over the graph. To demonstrate the scalability to large scale problems, a graph with 43826 nodes, which corresponds to a map of a maze in 2D, is considered in the simulation study. Apart from possible applications in robot path planning, the result is further extended to robot complete coverage, showing its potential in real practice such as cleaning robots.