An Optimization Approach to the Langberg-Médard Multiple Unicast Conjecture

Abstract

The Langberg-Médard multiple unicast conjecture claims that for any strongly reachable $k$-pair network, there exists a multi-flow with rate $(1,1,\dots ,1)$. In a previous work, through combining and concatenating the so-called elementary flows, we have constructed a multi-flow with rate at least $(\frac{8}{9},\frac{8}{9},\dots ,\frac{8}{9})$ for any $k$. In this paper, we examine an optimization problem arising from this construction framework. We first show that our previous construction yields a sequence of asymptotically optimal solutions to the aforementioned optimization problem. And furthermore, based on this solution sequence, we propose a perturbation framework, which not only promises a better solution for any $k\mathrm{mod}4\ne 2$ but also solves the optimization problem for the cases $k=3,4,\dots ,10$, accordingly yielding multi-flows with the largest rate to date.