Contents Special Topics in AI: Intelligent Agents and Multi-Agent - PowerPoint PPT Presentation

04/12/2012 Contents Special Topics in AI: Intelligent Agents and Multi-Agent Systems • Introduction • Auction Parameters • English, Dutch, and Vickrey Auctions Market Based Task Allocation: • Combinatorial Auctions Auctions – Winner Determination Problem (WDP) • Generalized Auctions – Google & Yahoo • Auction For Multi-Robot Exploration Alessandro Farinelli • Summary • Acknowledgment: material partly based on slides from Prof. Alex Kleiner, Linköping University Introduction I Introduction II • An auction takes place between an agent known as the • With the rise of the Internet, auctions have become popular auctioneer and a collection of agents known as the bidders in many e-commerce applications (e.g. eBay) – The goal of the auction is for the auctioneer to allocate • Auctions are an efficient tool for reaching agreements in a the good to one of the bidders society of self-interested agents – The auctioneer desires to maximize the price and – For example, bandwidth allocation on a network, sponsor bidders desire to minimize the price links • Dominant bidding strategy: A strategy for bidding that leads in the long-term to a maximal payoff • Auctions can be used for efficient resource allocation within • Bidder Payoff: valuation - payment decentralized computational systems • Valuation: The money you are willing to spent – Which do not necessarily consist of self-interested agents • Common or private value: Has the good a value – They are frequently utilized for solving multi-agent and acknowledged by everybody or do you assign a private multi-robot coordination problems value to it – For example, team-based exploration of unknown terrain 1

04/12/2012 Mechanism Design Auction Parameters I • Mechanism design protocol design (e.g. auctions) for multi-agent interactions with desirable properties, such as: • Good/Item valuation – Guaranteed success: Agreement is certain – Private value: good has different value for each agent, e.g., Jimi Hendrix’s guitar, Rino Gaetano’s guitar – Maximizing social welfare: Agreement maximizes sum – Public (common) value: good has the same value for all of utilities of all participating agents bidders, e.g., a new guitar – Pareto efficiency: There is no other outcome that will make at – Correlated value: value of goods depend on own private least one agent better off without making at least one other value and private value for other agents, e.g., buy agent worse off something with intention to sell it later (Hendix wins) – Individual Rationality/Stability: Following the protocol is in best • Payment determination interest of all agents (no incentive to cheat, deviate from – First price: Winner pays his bid protocol etc.) – Second price: Winner pays second-highest bid – Simplicity: Protocol makes for the agent appropriate • Secrecy of bids strategy „obvious“. (Agent can tractably determine – Open cry: All agent’s know all agent’s bids optimal strategy) – Sealed bid: No agent knows other agent’s bids – Distribution: no single point of failure; minimize communication Auction Parameters II English Auction • Auction procedure – One shot: Only one bidding round • English auctions are examples of first-price open-cry ascending auctions – Ascending: Auctioneer begins at minimum price, bidders increase bids • Protocol: – Descending: Auctioneer begins at price over value of good – Auctioneer starts by offering the good at a low price and lowers the price at each round – Auctioneer offers higher prices until no agent is willing to – Continuous: Internet pay the proposed level • Auctions may be – The good is allocated to the agent that made the highest – Standard Auction offer • One seller and multiple buyers • Properties – Reverse Auction – Generates competition between bidders • One buyer and multiple sellers (generates revenue for the seller when – Double Auction bidders are uncertain of their valuation) • Multiple sellers and multiple buyers – Dominant strategy: Bid slightly more than • Combinatorial Auctions current bit, withdraw if bid reaches personal valuation of good – Buyers and sellers may have combinatorial valuations for ������������������ ´ ´ � ´ ´ – Winner’s curse (for common value goods) bundles of goods 2

04/12/2012 The Winner’s curse Dutch Auction • Termed in the 1950s: • Dutch auctions are examples of first-price open-cry descending auctions – Oil companies bid for drilling rights in the Gulf of Mexico • Protocol: – Problem was the bidding process given the uncertainties in estimating the potential value of an offshore oil field – Auctioneer starts by offering the good at artificially high value – "Competitive bidding in high risk situations," by Capen, Clapp and Campbell, Journal of Petroleum Technology , – Auctioneer lowers offer price until some agent makes a bid 1971 equal to the current offer price • For example – The good is then allocated to the agent that made the offer – An oil field had an actual intrinsic value of $10 million – Oil companies might guess its value to be anywhere from ���������� • $5 million to $20 million – ���������������������� ���������� – The company who wrongly estimated at $20 million and ������������������������������ placed a bid at that level would win the auction, and later – ������������������������������������������ find that it was not worth that much ����������������������������������� ������������������������������������ • In many cases the winner is the person who has ����������������������������� overestimated the most � “The Winner’s curse” ������������������ ��������������������������� • Cure: Shade your bid by a certain amount – �������������� ������������� Vickrey Auctions First-Price Sealed-Bid Auctions • Proposed by William Vickrey in 1961 (Nobel Prize in Economic • First-price sealed-bid auctions are one-shot auctions : Sciences in 1996) • Vickrey auctions are examples of second-price sealed-bid one- • Protocol: shot auctions – Within a single round bidders submit a sealed bid for the • Protocol: good – within a single round bidders submit a sealed bid for the – The good is allocated to the agent that made highest bid good – Winner pays the price of highest bid – good is allocated to agent that made highest bid • Often used in commercial auctions, e.g., public building – winner pays price of second highest bid contracts etc. • Dominant strategy: bid your true valuation • Problem: the difference between the highest and second – if you bid more, you risk to pay too much highest bid is “wasted money” (the winner could have offered – if you bid less, you lower your chances of winning while less) still having to pay the same price in case you win • Intuitive strategy: bid a little bit less than your true valuation • Antisocial behavior: bid more than your true valuation to (no general dominant strategy) make opponents suffer (not “rational”) – As more bidders as smaller the deviation should be! 3