Compacting cuts: a new linear formulation for minimum cut

摘要

For a graph (V, E), existing compact linear formulations for the minimum cut problem require Θ(|V‖E|) variables and constraints and can be interpreted as a composition of |V| - 1 polyhedra for minimum s-t cuts in much the same way as early approaches to finding globally minimum cuts relied on |V| - 1 calls to a minimum s-t cut algorithm. We present the first formulation to beat this bound, one that uses O(|V|~2) variables and O(|V|~3) constraints. An immediate consequence of our result is a compact linear relaxation with O(|V|~2) constraints and O(|V|~3) variables for enforcing global connectivity constraints. This relaxation is as strong as standard cut-based relaxations and have applications in solving traveling salesman problems by integer programming as well as finding approximate solutions for survivable network design problems using Jain's iterative rounding method. Another application is a polynomial time verifiable certificate of size n for for the NP-complete problem of l_1-embeddability of a rational metric on an n-set (as opposed to one of size n~2 known previously).