Approximately-strategyproof and tractable multiunit auctions

We present an approximately-efficient and approximately-strategyproof auction mechanism for a single-good multiunit allocation problem. The bidding language allows marginal-decreasing piecewise-constant curves and quantity-based side constraints. We develop a fully polynomial-time approximation scheme for the multiunit allocation problem, which computes a (1+ε) approximation in worst-case time T=O(n3/ε), given n bids each with a constant number of pieces. We integrate this approximation scheme within a Vickrey-Clarke-Groves (VCG) mechanism and compute payments for an asymptotic cost of O(T log n). The maximal possible gain from manipulation to a bidder in the combined scheme is bounded by εV/(1+ε), where V is the total surplus in the efficient outcome.