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GAME THEORY
By: Rishika and Nithya 12/04/13
Outline
• What is game theory? • History of game theory • Basic concepts of game theory • Game theory and Informa8on Systems • Defini8on of Games • Nash Equilibrium • Applica8on of game theory in Power pools • The power transac8ons game • Costs and benefits in power transac8on • Conclusion • References
What is game theory? • It is the formal study of decision-‐making where several players must make choices that poten8ally affect the interests of the other players.
History of Game Theory
• Earliest example-‐study of duopoly by Antonie Cournot in 1838.
• In 1950-‐1960’s it broadened and was applied to problems of war and poli8cs. It has found applica8ons in sociology and psychology, and established links with evolu8on and biology.
• Received special aWen8on in 1994 with the awarding of the Nobel prize in economics to Nash.
• 1990’s-‐applica8on of game theory has been the design of auc8ons.
Basic Concepts of Game Theory
Players Nodes
Moves Pay-‐offs
Game
• Players-‐Players are independent decision-‐makers who influence the development of a game through their decisions.
• Nodes-‐As a game proceeds, various states of the world it is describing can be achieved. Such states are also called nodes.
• Move-‐A move allows the game to evolve from a well-‐defined state to another and therefore may indicate sequen8ality .
• Pay-‐offs-‐A payoff is a development of the game that the players value for itself according to their respec8ve preferences.
Game Theory and InformaLon Systems • The internal consistency and mathema8cal founda8ons of game theory make it a prime tool for modeling and designing automated decision-‐making processes in interac8ve environments.
• For example, one might like to have efficient bidding rules for an auc8on website.
• As a mathema8cal tool for the decision-‐maker the strength of game theory is the methodology it provides for structuring and analyzing problems of strategic choice.
DefiniLons of Games
Coopera8ve Non-‐coopera8ve
CooperaLve Game • In game theory, a cooperaLve game is a game where groups of players ("coali8ons") may enforce coopera8ve behavior, hence the game is a compe88on between coali&ons of players, rather than between individual players.
• For example, Recrea8onal games are rarely coopera8ve.
Non-‐cooperaLve Game • In game theory, a non-‐cooperaLve game is one in which players make decisions independently.
• Examples include Auc8on theory, Strategic vo8ng.
Extensive form game • The extensive form, also called a game tree, is more detailed than the strategic form of a game.
• It is a complete descrip8on of how the game is played over8me and includes the order in which players take ac8ons.
Example
Strategic form game • The strategic form game is usually represented by a matrix which shows the players, strategies, and pay-‐offs.
• More generally it can be represented by any func8on that associates a payoff for each player with every possible combina8on of ac8ons
Example
Nash Equilibrium • A set of strategies is a Nash equilibrium if no player can do beWer by unilaterally changing his or her strategy.
• Imagine that each player is told the strategies of the others Suppose then that each player asks himself or herself: "Knowing the strategies of the other players, and trea8ng the strategies of the other players as set in stone, can I benefit by changing my strategy?“
• If any player would answer "Yes", then that set of strategies is not a Nash equilibrium.
Structure of deregulated system
ApplicaLon of Game Theory for pricing Electricity in deregulated power pools • Independent System Operator receives bids by Pool par8cipants and defines transac8ons among par8cipants by looking for the minimum price that sa8sfies the demand in the Pool.
• As deregula8on evolves, pricing electricity becomes a major issue in the electric industry.
• In deregulated power systems, emphasis is given to benefit maximiza8on from the perspec8ve of par8cipants rather than maximiza8on of system-‐wide benefits.
The Pool Co
• Bids by generators as well as loads create a spot market for electricity.
• The spot price is set by the last generator dispatched by the IS0 to balance Pool Co.'s genera8on and demand.
• The objec8ve is to maximize each par8cipant’s benefits hence, earnings from transac8ons should be maximized.
• A seller has to evaluate the possibility of either selling more power at a low per unit price or selling less at a high price per unit of power. A similar analysis can be made for a buyer.
• Each par8cipant defines bids based on incomplete informa8on on other par8cipant’s bids.
The Power TransacLons Game • Game theory has been used in power systems to understand a par8cipant's behavior in deregulated environments and to allocate costs among Pool par8cipants.
• The game is assumed non-‐coopera8ve and the Nash equilibrium idea for non-‐coopera8ve games is used.
• In power transac8on game, par8cipants compete against each other to maximize their benefits.
• Economic benefits from transac8ons are the payoff of the game.
• The basic probability of the game is based on a random fuel price.
Costs and Benefits in Power TransacLons • Each par8cipant k has several generators and a total load Lk; in this case ƩPi0= Lk corresponds to the genera8on level before transac8ons are defined.
• The increment in cost incurred to change the genera8on level in is
• The marginal cost is given by
• The incremental cost and the marginal cost of generators are the linear func8ons of genera8on levels.
• The par8cipant’s bids are also linear func8ons of genera8on level.
• The IS0 receives par8cipants' bids as in equa8on and matches the lowest bid with the Pool Co.'s load.
• Power transac8on for par8cipant K is computed as
• The minimum price that matches genera8on and load is called the spot price of electricity ƿ.
• For a given spot price, the par8cipant’s benefit is
• Condi8on for benefit maximiza8on is
• • The par8cipant adjusts its genera8on so as in the absence of binding constraints:
• In a perfect compe00on, sellers and buyers are very small as compared with the market size; no par8cipant can significantly affect the exis8ng spot price.
Conclusion • In a perfect compe88on, the spot price in the Pool Co is essen8ally given and the op8mal price decision can be obtained without a game-‐theore8cal approach. Condi8ons of perfect compe88on are altered by several factors including network constraints.
• Game theory approaches have been used to study imperfect compe88on in electricity markets.
• Pricing electricity in deregulated pool is becoming a major issue in the electric industry and addi8onal mathema8cal support is needed to define pricing strategies in this environment.
• If we analyze the problem without a game-‐theore8cal approach, a par8cipant may obtain lower benefits than those obtained from the applica8on of the proposed method.
References
[1] Fudenberg, Drew and Tirole, Jean (1991), Game Theory. MIT Press, Cambridge, MA. [2] Gibbons, Robert (1992), Game Theory for Applied Economists. Princeton University Press, Princeton, NJ. [3] R. W. Ferrero, J. F. Rivera, and S. M. Shahidehpour, "Applica8on of games with incomplete informa8on for pricing electricity in deregulated power pools," Power Systems, IEEE Transac&ons on, vol. 13, pp. 184-‐189, 1998. [4] J.P. Aubin, “Mathema&cal Methods of Game and Economic Theory,” Amsterdam: North-‐Holland Publishing Company, 1982. [5] J . Harsanyi, “Games with Incomplete Informa8on,” The American Economic Review, Vol. 85, No. 3, June 1995, pp. 291-‐303.