Prior-free auctions for budgeted agents

  • Authors:
  • Nikhil R. Devanur;Bach Q. Ha;Jason D. Hartline

  • Affiliations:
  • Microsoft Research, Redmond, WA, USA;Northwestern University, Evanston, IL, USA;Northwestern University, Evanston, IL, USA

  • Venue:
  • Proceedings of the fourteenth ACM conference on Electronic commerce
  • Year:
  • 2013

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Abstract

We consider prior-free auctions for revenue and welfare maximization when agents have a common budget. The abstract environments we consider are ones where there is a downward-closed and symmetric feasibility constraint on the probabilities of service of the agents. These environments include position auctions where slots with decreasing click-through rates are auctioned to advertisers. We generalize and characterize the envy-free benchmark from Hartline and Yan [2011] to settings with budgets and characterize the optimal envy-free outcomes for both welfare and revenue. We give prior-free mechanisms that approximate these benchmarks. A building block in our mechanism is a clinching auction for position auction environments. This auction is a generalization of the multi-unit clinching auction of Dobzinski et al. [2008] and a special case of the polyhedral clinching auction of Goel et al. [2012]. For welfare maximization, we show that this clinching auction is a good approximation to the envy-free optimal welfare for position auction environments. For profit maximization, we generalize the random sampling profit extraction auction from Fiat et al. [2002] for digital goods to give a 10.0-approximation to the envy-free optimal revenue in symmetric, downward-closed environments. Even without budgets this revenue maximization question is of interest and we obtain an improved approximation bound of 7.5 (from 30.4 by Ha and Hartline [2012]).