1. Trading Agent Competition Bassam Aoun baoun@cs.uwaterloo.ca 08/11/2004

2. Outline TAC SCM Trading Agent Competition TacTex WhiteBear TAC classic Boticelli

3. Trading Agent Competition The TAC annual contest has been designed by –a team of researchers from the e-Supply Chain Management Lab at Carnegie Mellon University –the Swedish Institute of Computer Science (SICS). It offers agent designers a forum and a common platform to evaluate agents’ trading techniques It aims to spur research by –comparing the various approaches –enabling researchers to build over each other’s ideas;

4. TAC Games TAC-SCM, the Trading Agents Competition in a Supply Chain Management scenario, was designed to capture many of the challenges involved in supporting dynamic supply chain practices. TAC Classic - The software agents will represent travel coordinators whose goal is to arrange travel packages (flights, hotel rooms, and tickets to entertainment events) for clients.

5. Outline TAC SCM Trading Agent Competition TacTex WhiteBear TAC classic Boticelli

6. TAC SCM Game Overview

7. Agent Daily Events

8. Tracking Agents…

9. TacTex vs. Boticelli Similarities: TacTex and Botticelli build models of the environment and attempt to optimize with respect to those models Differences: Given computational complexity –TacTex proposes greedy heuristics –Boticelli proposes Sample Average Approximation (SAA) What if there are any production cycles remaining? –TacTex uses them to build up an equal inventory of all computer types to be used to satisfy future orders. –Boticelli uses stochastic approach to predict future customer orders through scenarios

10. Outline TAC SCM Trading Agent Competition TacTex WhiteBear TAC classic Boticelli

11. Starting Point Formulate optimal solutions for major decisions Used linear programming that plans for the next several days of production They referred to [Benisch et al. 2004] Unfortunately, it failed to produce a result within the 15 seconds available per game day. Proposed a greedy heuristic approach

12. The greedy production scheduler Divide the current orders into two lists: –orders that are late or will be late if not produced immediately –all other orders Sort each list in order of decreasing value Rank by (price − cost + penalties) Append the second list to the first Go through the list attempting to fill each order: –Use any computers in inventory that are available –See if the remaining amount needed can be produced –If the order can be filled, earmark the computers for delivery

13. The first-day ordering strategy On the first day: (Supply are cheapest) –send RFQs: 8800, 4400, 2200, 1100, and 550 of each component (To maintain flexibility) On the second day: –predict the number of components needed based on the number of customer RFQs Prediction based on day #2 RFQ  Total RFQs –project total future production using the offered components to find the usable amount –accept a subset of the offers providing the desired amount

14. After day #1… Need a different strategy after day 1 (if more needed) Prices are determined by due date –Supplier has lots of orders before due date  high price Probe price as function of due date with small RFQs Request enough to maintain threshold supply 50 days ahead (assuming current rate of use) Only accept if expected profit increase > price –Marginal value based on assumptions about computer prices and other components’ costs

15. Offering Computers Find the set of offers that maximizes profit Need to estimate P( winning order | offer price) Given RFQ and cost of computer in question, optimal price maximizes  (price - cost) * P( order | price) May not be able to produce all orders for optimal prices –Then need to raise prices to reduce demand Iteratively raise prices on the least profitable offers Repeat until all orders can be produced Too many orders  less capacity for future order

16. Summary Very little opportunity for optimal decision- making Lots of prediction in their strategy Many attempts at learning and adaptation So far only a few are useful –Predicting future customers’ RFQs is difficult (e.g. quantity and day factors) –Predicting the acceptance of an offer P( order | price) –Number of days to look into the future such that the model is still valid

17. Outline TAC SCM Trading Agent Competition TacTex WhiteBear TAC classic Boticelli

18. The Botticelli Agent This paper addresses scheduling component of the TAC SCM problem. Use stochastic information in the form of probabilistic models built from historical data Formulate the problem as a stochastic program Optimize solution using sample average approximation (SAA) Maximize expected profit, given a prior for each RFQ (how likely is it to become an order)

19. Expected Production Scheduling Input –Bidding policy, product prices, orders, RFQs, procurement schedule, inventory, historical data… Objective –maximize order profits and expected offer profits Constraint –Quantity of SKU j in orders or expected offers delivered by day t cannot exceed amount of SKU j produced by day (t-1) + initial inventory

20. Simple Scheduling Problem Given: Orders (SKU, quantity, due date, penalty, price) Inventory Procurement schedule Number of production cycles per product Product specification Find: Production schedule that optimizes profit

21. ILP Solution Constants o – set of orders Order i = { SKU s i, price p i, quantity q i, due date d i, penalty ρ i, reserve price r i } The profit π il for filling order i on day l a k – quantity of component k in initial inventory b j – quantity of SKU j in initial inventory C – machine capacity in production cycles c j – number of production cycles for SKU j e jk – indicator, is component k part of SKU j

22. ILP Solution Variables z il – indicates whether or not order i is filled on day l y jl – amount of SKU j scheduled for production on day l

23. ILP Objective function and constraints (1) (2) (4) (3) (5) Such that:

24. Stochastic Programming Extending the simple model by adding a set of RFQs Each RFQ is given a prior α i, according to historical information, indicating its probability of becoming an order. Given a set of orders, and a set of RFQs today, only a fraction of which will be realized tomorrow Goal to produce an optimal set of SKUs today, such that tomorrow’s profits will be maximized.

25. Additional variables & constants Constants Ω m – set of possible scenarios Variables z ilm – indicates whether or not RFQ i is filled on day l in scenario m y jlm – amount of SKU j scheduled for production on day l in scenario m w i – indicates whether or not order i is filled on day 1 v j – amount of SKU j scheduled for production on day 1

26. Objective function & constraints s.t. Stage 1 Stage 2

27. Approximation algorithms

28. Expected Profit/Quantity/Value algorithms Solve variants of the simple scheduling problem Expected profits algorithm uses expected profits, calculated by multiplying π il by α i Expected quantities algorithm uses expected quantities, calculated by multiplying q i by α i Expected value uses expected profits and expected quantities

29. Sample Average Approximation Sample the scenario space (used 30 samples in the paper), and optimize a regular ILP problem: SAA-Greedy –Samples scenarios with RFQs for only one day, –Do not reason about future RFQs SAA-Average and SAA-Sampling –Sample scenarios with RFQs for N days, –They differ on how to sample future RFQs.

30. Not-In-Time Algorithm Ignores stochastic information completely Schedules only orders, i.e., realized RFQs Production does not begin until one day after RFQs are received – can lead to late penalties

31. Metrics Used P – mean profit per order C – Percentage of cycles used to fill orders P/C – profit per cycle EVPI – Expected value of perfect information VSI – Value of stochastic information

32. Results for the 7 algorithms

33. Conclusions 1.The stochastic programs outperformed all of the other schedulers (in all except one metric) 2.Stochastic algorithms that rely on forecasts about future RFQs outperformed SAAG 1.Using stochastic information improves performance 2.Utilizing more stochastic information about the future leads to better performance

34. Outline TAC SCM Trading Agent Competition TacTex WhiteBear TAC classic Boticelli

35. Bidding in Simultaneous Auctions Goods are traded independently Different rules for each auction (potentially) Main issue: Participants need to speculate on behavior of other agents How aggressively does one bid, when and what for? Having a plan flexible enough to handle contingencies Best solution is relative to other players strategies

36. TAC Classic General problem capturing several issues of bidding in simultaneous auctions Provides a universal testbed for researchers Travel agents –Working on behalf of 8 customers each The type of each agent is determined by the preferences by its clients. –Arranging for a trip to Tampa round-trip flight tickets hotel accommodations entertainment tickets –GOAL: Maximize clients’ utilities

37. TAC Classic URL: www.sics.se/tacwww.sics.se/tac

38. Outline TAC SCM Trading Agent Competition TacTex WhiteBear TAC classic Boticelli

39. General Architecture (Modular) Follows the Sense Model Plan Act (SMPA) architecture While (not end of game) { Get price quotes Calculate estimates & statistics Planner (Formulate desired plan) Bidder (Bid to implement plan) } Challenges: –The quantity of each good to be bought –The prices offered for each individual unit –The times at which the bids are placed.

40. Determining Partial Strategies Determine “boundary strategies” –E.g. minimum and maximum price for the bid, if bid price is the issue Determine “intermediate strategies” –By modifying boundary strategies –By combining boundary strategies –By using a strategy that constitutes an equilibrium for a simpler but similar game

41. Bidding Strategies – Hotels Auction Rules: Ascending and multi-unit auctions with price quotes announced periodically. One randomly selected auction closes at minutes 4 to 11 (one each minutes). Issue: Bid Price Dilemma: If not aggressive, could get outbid and lose rooms needed –will get outbid by other agents and lose utility for not implementing the plan and for unused resources If too aggressive, prices will skyrocket and the agent’s score will get hurt more than other agents’ scores –All agents’ scores are hurt –But this hurts the agent more, since rooms it desires will have an increased price

42. Bidding Strategies – Hotels (cont.) 1.Low aggressiveness : (boundary str.)  Bids higher than the current ask price by an increment 2.High aggressiveness : (boundary str.)  Bids for all rooms progressively closer to the marginal utility 3.Medium aggressiveness : (intermediate str.)  Combines two previous strategies  For critical rooms (rooms with high marginal utility) the bid is close to the marginal utility  For all other rooms it bids an increment above the current price (the increment increases as time passes)

43. Bidding – Plane Tickets Auction Rules: Ticket prices are expected to increase approximately in proportion to the square of the time elapsed since the start of the game Issue: Time of Bid Placement Dilemma: –To bid early in order to get the cheapest tickets –Or to bid later in order not to limit its options Solution: Bid for some of the tickets at the beginning Bids for the rest after some hotel room auctions have closed Strategies: Which tickets are bought at the beginning

44. Bidding – Plane Tickets (cont.) 1.Late Bidder : (boundary str.)  Buy at the beginning only tickets that are “certain” to be used 2.Early Bidder : (boundary str.)  Buy all tickets at the beginning 3.Strategic Bidder : (intermediate str.)  Modifies “Early Bidder” boundary strategy  Uses “Strategic Demand Reduction”  Buy all tickets at the beginning, except the ones that are “highly likely not to be used”

45. Decomposing the Problem Optimizer / Planner Auction Type 1 Partial Bidding Strategy 1 Auction Type 2 Partial Bidding Strategy 2 Auction Type k Partial Bidding Strategy k Agent

46. Exploring Strategy Space Determine the best partial strategy for one particular auction type –Keep all other partial strategies fixed –Use a fixed number of agents using intermediate strategies –Vary the mixture of agents using boundary strategies Explore strategy space systematically –Use several experiments to evaluate the strategies for different auction types –Use the best partial strategies found in the previous experiments as the strategies that are kept fixed in each experiment –Stop when experiments “converge”

47. Experimental Results  Overall the medium and high aggressiveness versions perform the best –But the medium aggressiveness agent is more consistent in general  Overall the strategic agent versions perform the best –The early bidder is significantly better than the late bidder  In general you win when you are “going against the tide”, i.e. being aggressive when most other agents are not

48. General Observations Planner is adaptive, versatile, fast and robust Agent uses both principled methods and approaches guided by the knowledge acquired by observing the behavior of the games and combines both seamlessly The agent used in TAC was the strategic agent with medium aggressiveness Agent White Bear always ranks in the top three agents in all the competition rounds of the Trading Agent Competition

49. TAC Classic 2002- 2004 #Agent (2004)Score 1WhiteBear4122 2Walverine3849 3LearnAgents3737 #Agent (2002)Score 1WhiteBear3556 2Southampton3492 3Thalis3351 #Agent (2003)Score 1ATTac013200 2PackaTAC3163 3WhiteBear3142

50. References The Supply Chain Management Game for the Trading Agent Competition 2004 (Aranuchalam et al. 2004) TacTex03 - A supply chain management agent, (Pardoe et al. 2004) A Stochastic Programming Approach to Scheduling in TAC-SCM (Benisch et al. 2004) A principled study of design tradeoffs for autonomous trading agents, (Ioannis et al. 2003)