MoN11: Eleventh Mathematics of Networks meeting, 20th July University of Warwick

Timothy G. Griffin (University of Cambridge) – Local optimality in algebraic path problems, with help from Coq + Ssreflect.

Due to complex policy constraints, some Internet routing protocols are associated with non-standard metrics that fall outside of the approach to path problems based on semirings and “globally optimal” paths. Some of these exotic metrics can be captured by relaxing the semiring axioms to include algebras that are not distributive. A notion of “local optimality” can be defined for such algebras as a fixed-point of a matrix equation, and this models well they type of solutions required by Internet routing protocols.

In this talk I’ll present a proof that Dijkstra’s algorithm can be used to solve path problems for local optimality over some non-distributive algebras. A proof of this appeared in [1], but I will discuss a more recent proof done with the Coq [2] theorem prover and the Ssreflect [3] extension. I’ll comment on my experiences using these tools and suggest that others may find them helpful in formalising combinatorial algorithms.

[1] Routing in Equilibrium. João Luís Sobrinho and Timothy G. Griffin. The 19th International Symposium on Mathematical Theory of Networks and Systems (MTNS 2010)



Return to previous page

Contact: Keith Briggs (mailto:keith.briggs_at_bt_dot_com) or Richard G. Clegg (