Spreading random connection functions Massimo Franceschetti Newton Institute for Mathematical Sciences April, 7, 2010 joint work with Mathew Penrose and Tom Rosoman
The result in a nutshell In networks generated by Random Connection Models in Euclidean space, occasional long-range connections can be exploited to achieve connectivity (percolation) at a lower node density value
Bond percolation on the square grid
The holy grail
Site percolation on the square grid
Still very far from the holy grail Grimmett and Stacey (1998) showed that this inequality holds for a wide range of graphs beside the square grid
Proof of by dynamic coupling Can reach anywhere inside a green site percolation cluster via a subset of the open edges in the edge percolation model The same procedure works for any graph, not only the grid
Poisson distribution of points of density λ points within unit range are connected S D Gilbert graph A continuum version of a percolation model
Simplest communication model A connected component represents nodes which can reach each other along a chain of successive relayed communications
The critical density
Random Connection Model
Simple model for unreliable communication
Question
The expected node degree is preserved but connections are spatially stretched Spreading transformation
Weak inequality
Proof sketch of weak inequality
Strict inequality It follows that the approach to this limit is strictly monotone from above and spreading is strictly advantageous for connectivity
Main tools for the proof of The key technique is enhancement Menshikov (1987), Aizenman and Grimmett (1991), Grimmett and Stacey (1998) We also need the inequality for RCM graphs which are not included in Grimmett and Staceys family (see Mathews talk on Friday) And use of a dynamic construction of the Poisson point process and some scaling arguments
Proof sketch of strict inequality
Spread-out annuli
Mixture of short and long edges Edges are made all longer Spread-out visualisation
Spread-out dimension
Open problems Monotonicity of annuli-spreading and dimension- spreading Monotonicity of spreading in the discrete setting
Conclusion Main philosophy is to compare different RCM percolation thresholds rather than search for exact values in specific cases In real networks spread-out long-range connections can be exploited to achieve connectivity at a strictly lower density value Thank you!