{"id":330617,"date":"2016-12-01T22:16:58","date_gmt":"2016-12-02T06:16:58","guid":{"rendered":"https:\/\/www.microsoft.com\/en-us\/research\/?post_type=msr-research-item&#038;p=330617"},"modified":"2018-10-16T20:34:14","modified_gmt":"2018-10-17T03:34:14","slug":"learning-auctions-regret-hard-envy-easy","status":"publish","type":"msr-research-item","link":"https:\/\/www.microsoft.com\/en-us\/research\/publication\/learning-auctions-regret-hard-envy-easy\/","title":{"rendered":"Learning in Auctions: Regret is Hard, Envy is Easy"},"content":{"rendered":"<p>A large line of recent work studies the welfare guarantees of simple and prevalent combinatorial auction formats, such as selling m items via simultaneous second price auctions (SiSPAs) [CKS08, BR11, FFGL13]. These guarantees hold even when the auctions are repeatedly executed and the players use no-regret learning algorithms to choose their actions. Unfortunately, off-the-shelf no-regret learning algorithms for these auctions are computationally inefficient as the number of actions available to each player is exponential. We show that this obstacle is insurmountable: there are no polynomial-time no-regret learning algorithms for SiSPAs, unless RP \u2287 NP, even when the bidders are unit-demand. Our lower bound raises the question of how good outcomes polynomially-bounded bidders may discover in such auctions. To answer this question, we propose a novel concept of learning in auctions, termed \u201cnoenvy learning.\u201d This notion is founded upon Walrasian equilibrium, and we show that it is both efficiently implementable and results in approximately optimal welfare, even when the bidders have valuations from the broad class of fractionally subadditive (XOS) valuations (assuming demand oracle access to the valuations) or coverage valuations (even without demand oracles). No-envy learning outcomes are a relaxation of no-regret learning outcomes, which maintain their approximate welfare optimality while endowing them with computational tractability. Our result for XOS valuations can be viewed as the first instantiation of approximate welfare maximization in combinatorial auctions with XOS valuations, where both the designer and the agents are computationally bounded and agents are strategic. Our positive and negative results extend to many other simple auction formats that have been studied in the literature via the smoothness paradigm. Our positive results for XOS valuations are enabled by a novel Follow-The-Perturbed-Leader algorithm for settings where the number of experts and states of nature are both infinite, and the payoff function of the learner is non-linear. We show that this algorithm has applications outside of auction settings, establishing big gains in a recent application of no-regret learning in security games. Our efficient learning result for coverage valuations is based on a novel use of convex rounding schemes and a reduction to online convex optimization.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>A large line of recent work studies the welfare guarantees of simple and prevalent combinatorial auction formats, such as selling m items via simultaneous second price auctions (SiSPAs) [CKS08, BR11, FFGL13]. These guarantees hold even when the auctions are repeatedly executed and the players use no-regret learning algorithms to choose their actions. Unfortunately, off-the-shelf no-regret 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