New strategy: Collective Strategy

Author: marcharper

axelrod/strategies/_strategies.py

@@ -52,8 +52,8 @@
 from .mutual import Desperate, Hopeless, Willing
 from .negation import Negation
 from .oncebitten import OnceBitten, FoolMeOnce, ForgetfulFoolMeOnce, FoolMeForever
-from .prober import (Prober, Prober2, Prober3, Prober4, HardProber,
-                     NaiveProber, RemorsefulProber)
+from .prober import (CollectiveStrategy, Prober, Prober2, Prober3, Prober4,
+                     HardProber, NaiveProber, RemorsefulProber)
 from .punisher import Punisher, InversePunisher
 from .qlearner import (
     RiskyQLearner, ArrogantQLearner, HesitantQLearner, CautiousQLearner)
@@ -92,6 +92,7 @@
     Calculator,
     CautiousQLearner,
     Champion,
+    CollectiveStrategy,
     ContriteTitForTat,
     Cooperator,
     CooperatorHunter,

axelrod/strategies/prober.py

@@ -5,6 +5,42 @@
 C, D = Actions.C, Actions.D
 
 
+class CollectiveStrategy(Player):
+    """Defined in [Li2009]. 'It always cooperates in the first move and defects
+    in the second move. If the opponent also cooperates in the first move and
+    defects in the second move, CS will cooperate until the opponent defects.
+    Otherwise, CS will always defect.'
+
+    Names:
+        Collective Strategy [Li2009]
+
+    """
+
+    name = "CollectiveStrategy"
+
+    classifier = {
+        'stochastic': False,
+        'memory_depth': float('inf'),  # Long memory
+        'makes_use_of': set(),
+        'long_run_time': False,
+        'inspects_source': False,
+        'manipulates_source': False,
+        'manipulates_state': False
+    }
+
+    def strategy(self, opponent):
+        turn = len(self.history)
+        if turn == 0:
+            return C
+        if turn == 1:
+            return D
+        if opponent.defections > 1:
+            return D
+        if opponent.history[0:2] == [C, D]:
+            return C
+        return D
+
+
 class Prober(Player):
     """
     Plays D, C, C initially. Defects forever if opponent cooperated in moves 2

axelrod/tests/unit/test_prober.py

@@ -8,6 +8,34 @@
 C, D = axelrod.Actions.C, axelrod.Actions.D
 
 
+class TestCollectiveStrategy(TestPlayer):
+
+    name = "CollectiveStrategy"
+    player = axelrod.CollectiveStrategy
+    expected_classifier = {
+        'memory_depth': float('inf'),
+        'stochastic': False,
+        'makes_use_of': set(),
+        'long_run_time': False,
+        'inspects_source': False,
+        'manipulates_source': False,
+        'manipulates_state': False
+    }
+
+    def test_initial_strategy(self):
+        """Starts by playing CD."""
+        self.responses_test([], [], [C, D])
+
+    def test_strategy(self):
+        # Defects forever unless opponent matched first two moves
+        self.responses_test([C, D], [C, C], [D] * 10)
+        self.responses_test([C, D], [D, C], [D] * 10)
+        self.responses_test([C, D], [D, D], [D] * 10)
+
+        self.responses_test([C, D], [C, D], [C] * 10)
+        self.responses_test([C, D, D], [C, D, D], [D] * 10)
+
+
 class TestProber(TestPlayer):
 
     name = "Prober"

docs/reference/bibliography.rst

@@ -19,6 +19,7 @@ documentation.
 .. [Frean1994] Frean, Marcus R. “The Prisoner's Dilemma without Synchrony.” Proceedings: Biological Sciences, vol. 257, no. 1348, 1994, pp. 75–79. www.jstor.org/stable/50253.
 .. [Hilde2013] Hilbe, C., Nowak, M.A. and Traulsen, A. (2013). Adaptive dynamics of extortion and compliance, PLoS ONE, 8(11), p. e77886. doi: 10.1371/journal.pone.0077886.
 .. [Kraines1989] Kraines, D. & Kraines, V. Theor Decis (1989) 26: 47.  doi:10.1007/BF00134056
+.. [Li2009] Li, J. & Kendall, G. (2009). A Strategy with Novel Evolutionary Features for the Iterated Prisoner’s Dilemma. Evolutionary Computation 17(2): 257–274.
 .. [Li2011] Li, J., Hingston, P., Member, S., & Kendall, G. (2011). Engineering Design of Strategies for Winning Iterated Prisoner ’ s Dilemma Competitions, 3(4), 348–360.
 .. [Li2014] Li, J. and Kendall, G. (2016). The Effect of Memory Size on the Evolutionary Stability of Strategies in Iterated Prisoner's Dilemma. IEEE Transactions on Evolutionary Computation, 18(6) 819-826
 .. [Nachbar1992] Nachbar J., Evolution in the finitely repeated prisoner’s dilemma, Journal of Economic Behavior & Organization, 19(3): 307-326, 1992.