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strategy (Definition)

A pure strategy provides a complete definition for a way a player can play a game. In particular, it defines, for every possible choice a player might have to make, which option the player picks. A player's strategy space is the set of pure strategies available to that player.

A mixed strategy is an assignment of a probability to each pure strategy. It defines a probability over the strategies, and reflect that, rather than choosing a particular pure strategy, the player will randomly select a pure strategy based on the distribution given by their mixed strategy. Of course, every pure strategy is a mixed strategy (the function which takes that strategy to $ 1$ and every other one to 0).

The following notation is often used:

  • $ S_i$ for the strategy space of the $ i$-th player
  • $ s_i$ for a particular element of $ S_i$; that is, a particular pure strategy
  • $ \sigma_i$ for a mixed strategy. Note that $ \sigma_i\in S_i\rightarrow [0,1]$ and $ \sum_{s_i\in S_i} \sigma_i(s_i)=1$.
  • $ \Sigma_i$ for the set of all possible mixed strategies for the $ i$-th player
  • $ S$ for $ \prod_i S_i$, the set of all possible combinations of pure strategies (essentially the possible outcomes of the game)
  • $ \Sigma$ for $ \prod_i \Sigma_i$
  • $ \sigma$ for a strategy profile, a single element of $ \Sigma$
  • $ S_{-i}$ for $ \prod_{j\neq i} S_j$ and $ \Sigma_{-i}$ for $ \prod_{j\neq i} \Sigma_j$, the sets of possible pure and mixed strategies for all players other than $ i$.
  • $ s_{-i}$ for an element of $ S_{-i}$ and $ \sigma_{-i}$ for an element of $ \Sigma_{-i}$.



"strategy" is owned by Henry.
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See Also: game

Also defines:  strategy, pure strategy, mixed strategy, strategy space
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Cross-references: outcomes, function, distribution, reflect, game, player
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This is version 4 of strategy, born on 2002-07-24, modified 2002-07-28.
Object id is 3204, canonical name is Strategy2.
Accessed 11614 times total.

Classification:
AMS MSC91A99 (Game theory, economics, social and behavioral sciences :: Game theory :: Miscellaneous)

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