EvoLudoLab: 2x2 Game - Coexistence
Along the bottom of the applet there are several buttons to control the execution and the speed of the simulations - for details see the EvoLudo GUI documentation. Of particular importance are the parameters button and the data views pop-up list along the top. The former opens a panel that allows to set and change various parameters concerning the game as well as the population structure, while the latter displays the simulation data in different ways.
|New cooperator||New defector|
Note: The shades of grey of the payoff scale are augmented by blueish and reddish shades indicating payoffs for mutual cooperation and defection, respectively.
Type A and type B co-exist
Almost independently of the initial configuration, the population quickly converges to a mixed state where type <math>A</math> and <math>B</math> players co-exist.
In the context of cooperation, this scenario is captured by the Snowdrift Game, the Hawk-Dove Game or the Chicken Game: the best strategic option depends on the co-player - if he/she defects, it is better to cooperate but if he/she cooperates then defection pays off. Consequently, in a well-mixed population the rare type is always favored and hence cooperators and defectors co-exist in a stable equilibrium. Such interactions indicate another, slightly relaxed form of a social dilemma.
The above parameters are set to <math>R = 1, P = 0, T = 1.62</math> and <math>S = -0.38</math> with players imitating better strategies proportional to the payoff difference and an initial fraction of cooperators of 99% in a population of size 10'000.
|Snapshot of the spatial arrangement of strategies.|
|Time evolution of the strategy frequencies.|
|Snapshot of the spatial distribution of payoffs.|
|Time evolution of average population payoff bounded by the minimum and maximum individual payoff.|
|Snapshot of payoff distribution in population.|
|Degree distribution in structured populations.|
|Message log from engine.|
The list below describes only the few parameters related to the Prisoner's Dilemma, Snowdrift and Hawk-Dove games. Follow the link for a complete list and detailed descriptions of the user interface and further parameters such as spatial arrangements or update rules on the player and population level.
- reward for mutual cooperation.
- temptation to defect, i.e. payoff the defector gets when matched with a cooperator. Without loss of generality two out of the four traditional payoff values \(R, S, T\) and \(P\) can be fixed and set conveniently to \(R = 1\) and \(P = 0\). This means mutual cooperation pays \(1\) and mutual defection zero. For example for the prisoner's dilemma \(T > R > P > S\) must hold, i.e. \(T > 1\) and \(S < 0\).
- sucker's payoff which denotes the payoff the cooperator gets when matched with a defector.
- punishment for mutual defection.
- Init Coop, init defect
- initial fractions of cooperators and defectors. If they do not add up to 100%, the values will be scaled accordingly. Setting the fraction of cooperators to 100% and of defectors to zero, then the lattice is initialized with a symmetrical configuration suitable for observing evolutionary kaleidoscopes.