Overrelaxed Sinkhorn–Knopp Algorithm for Regularized Optimal Transport

• Main Authors: Alexis Thibault, Lénaïc Chizat, Charles Dossal, Nicolas Papadakis
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Algorithms
• Subjects: optimal transport; Sinkhorn–Knopp algorithm; overrelaxation
• Online Access: https://www.mdpi.com/1999-4893/14/5/143

This article describes a set of methods for quickly computing the solution to the regularized optimal transport problem. It generalizes and improves upon the widely used iterative Bregman projections algorithm (or Sinkhorn–Knopp algorithm). We first proposed to rely on regularized nonlinear acceleration schemes. In practice, such approaches lead to fast algorithms, but their global convergence is not ensured. Hence, we next proposed a new algorithm with convergence guarantees. The idea is to overrelax the Bregman projection operators, allowing for faster convergence. We proposed a simple method for establishing global convergence by ensuring the decrease of a Lyapunov function at each step. An adaptive choice of the overrelaxation parameter based on the Lyapunov function was constructed. We also suggested a heuristic to choose a suitable asymptotic overrelaxation parameter, based on a local convergence analysis. Our numerical experiments showed a gain in convergence speed by an order of magnitude in certain regimes.