bimatrix game

class="infobox"

| \mathbf{A} = \begin{bmatrix}

c & d & e \\

f & g & h \\

\end{bmatrix}

| \mathbf{B} = \begin{bmatrix}

p & q & r \\

s & t & u \\

\end{bmatrix}

colspan="2"|

\begin{array}{c|c|c|c} & X & Y & Z \\

\hline

V & c,p & d,q & e,r \\

W & f,s & g,t & h,u \\

\end{array}

A payoff matrix converted from A and B where player 1 has two possible actions V and W and player 2 has actions X, Y and Z

In game theory, a bimatrix game is a simultaneous game for two players in which each player has a finite number of possible actions. The name comes from the fact that the normal form of such a game can be described by two matrices - matrix A describing the payoffs of player 1 and matrix B describing the payoffs of player 2.{{cite web | url=http://www.utdallas.edu/~chandra/documents/6311/bimatrix.pdf | title=Bimatrix games | accessdate=17 December 2015 | author=Chandrasekaran, R}}

Player 1 is often called the "row player" and player 2 the "column player". If player 1 has m possible actions and player 2 has n possible actions, then each of the two matrices has m rows by n columns. When the row player selects the i-th action and the column player selects the j-th action, the payoff to the row player is A[i,j] and the payoff to the column player is B[i,j].

The players can also play mixed strategies. A mixed strategy for the row player is a non-negative vector x of length m such that: \sum_{i=1}^m x_i = 1. Similarly, a mixed strategy for the column player is a non-negative vector y of length n such that: \sum_{j=1}^n y_j = 1. When the players play mixed strategies with vectors x and y, the expected payoff of the row player is: x^\mathsf{T} A y and of the column player: x^\mathsf{T} B y.

Nash equilibrium in bimatrix games

Every bimatrix game has a Nash equilibrium in (possibly) mixed strategies. Finding such a Nash equilibrium is a special case of the Linear complementarity problem and can be done in finite time by the Lemke–Howson algorithm.

There is a reduction from the problem of finding a Nash equilibrium in a bimatrix game to the problem of finding a competitive equilibrium in an economy with Leontief utilities.{{Cite book|doi=10.1145/1109557.1109629|chapter=Leontief economies encode nonzero sum two-player games|title=Proceedings of the seventeenth annual ACM-SIAM symposium on Discrete algorithm - SODA '06|pages=659|year=2006|last1=Codenotti|first1=Bruno|last2=Saberi|first2=Amin|last3=Varadarajan|first3=Kasturi|last4=Ye|first4=Yinyu|isbn=0898716055}}

Related terms

A zero-sum game is a special case of a bimatrix game in which A+B = 0.

References