Fast Monotone 3-Approximation Algorithm for Scheduling Related Machines

We consider the problem of scheduling n jobs to m machines of different speeds s.t. the makespan is minimized (Q||Cmax). We provide a fast and simple, deterministic monotone 3-approximation algorithm for Q||Cmax. Monotonicity is relevant in the context of truthful mechanisms: when each machine speed is only known to the machine itself, we need to motivate that machines declare their true speeds to the scheduling mechanism. As shown by Archer and Tardos, such motivation is possible only if the scheduling algorithm used by the mechanism is monotone. The best previous monotone algorithm that is polynomial in m, was a 5-approximation by Andelman et al. A randomized 2-approximation method, satisfying a weaker definition of truthfulness, is given by Archer. As a core result, we prove the conjecture of Auletta et al., that the greedy algorithm (Lpt) is monotone if machine speeds are all integer powers of 2.