FIX: Disallow Player with 0 actions

quantecon/game_theory/normal_form_game.py

@@ -168,6 +168,8 @@ def __init__(self, payoff_array):
 
         if self.payoff_array.ndim == 0:
             raise ValueError('payoff_array must be an array_like')
+        if np.prod(self.payoff_array.shape) == 0:
+            raise ValueError('every player must have at least one action')
 
         self.num_opponents = self.payoff_array.ndim - 1
         self.num_actions = self.payoff_array.shape[0]
@@ -418,6 +420,8 @@ def is_dominated(self, action, tol=None, method=None):
         ind[action] = False
         D = payoff_array[ind]
         D -= payoff_array[action]
+        if D.shape[0] == 0:  # num_actions == 1
+            return False
         if self.num_opponents >= 2:
             D.shape = (D.shape[0], np.prod(D.shape[1:]))
 

quantecon/game_theory/tests/test_normal_form_game.py

@@ -376,6 +376,24 @@ def test_normalformgame_setitem_1p():
     eq_(g.players[0].payoff_array[0], 10)
 
 
+# Trivial cases with one action #
+
+class TestPlayer_1action:
+    def setUp(self):
+        """Setup a Player instance"""
+        self.payoffs = [[0, 1]]
+        self.player = Player(self.payoffs)
+
+    def test_is_dominated(self):
+        for action in range(self.player.num_actions):
+            for method in LP_METHODS:
+                eq_(self.player.is_dominated(action, method=method), False)
+
+    def test_dominated_actions(self):
+        for method in LP_METHODS:
+            eq_(self.player.dominated_actions(method=method), [])
+
+
 # Test __repr__ #
 
 def test_player_repr():
@@ -393,6 +411,11 @@ def test_player_repr():
 
 # Invalid inputs #
 
+@raises(ValueError)
+def test_player_zero_actions():
+    p = Player([[]])
+
+
 @raises(ValueError)
 def test_normalformgame_invalid_input_players_shape_inconsistent():
     p0 = Player(np.zeros((2, 3)))
@@ -424,6 +447,11 @@ def test_normalformgame_invalid_input_payoff_profiles():
     g = NormalFormGame(np.zeros((2, 2, 1)))
 
 
+@raises(ValueError)
+def test_normalformgame_zero_actions():
+    g = NormalFormGame((2, 0))
+
+
 # Utility functions #
 
 def test_pure2mixed():