Convergence rate and termination of asynchronous iterative algorithms

We consider iterative algorithms of the form x := ƒ(x), executed by a parallel or distributed computing system. We focus on asynchronous implementations whereby each processor iterates on a different component of x, at its own pace, using the most recently received (but possibly outdated) information on the remaining components of x. We provide results on the convergence rate of such algorithms and make a comparison with the convergence rate of the corresponding synchronous methods in which the computation proceeds in phases. We also present results on how to terminate asynchronous iterations in finite time with an approximate solution of the computational problem under consideration.