Node values are well-defined!

Author: tturocy

ChangeLog

@@ -5,7 +5,7 @@
 ### Changed
 - `Game.comment` has been renamed to `Game.description`
 - With behaviour profiles that reach some information sets with probability zero, beliefs, action
-  values, infoset values, and node values are not well-defined.  These functions now return a
+  values, and infoset values are not well-defined.  These functions now return a
   `std::optional` in C++ and type or `None` in Python, where nulls indicate these quantities
   are not defined.  (#446)
 

src/games/behavmixed.cc

@@ -311,15 +311,12 @@ template <class T> Vector<T> MixedBehaviorProfile<T>::GetPayoff(const GameNode &
 }
 
 template <class T>
-std::optional<T> MixedBehaviorProfile<T>::GetPayoff(const GamePlayer &p_player,
-                                                    const GameNode &p_node) const
+const T &MixedBehaviorProfile<T>::GetPayoff(const GamePlayer &p_player,
+                                            const GameNode &p_node) const
 {
   CheckVersion();
   EnsureNodeValues();
-  if (p_node->GetInfoset() && GetInfosetProb(p_node->GetInfoset()) == T{0}) {
-    return std::nullopt;
-  }
-  return m_cache.m_nodeValues[p_node][p_player];
+  return m_cache.m_nodeValues.at(p_node).at(p_player);
 }
 
 template <class T>

src/games/behavmixed.h

@@ -243,7 +243,7 @@ template <class T> class MixedBehaviorProfile {
   T GetInfosetProb(const GameInfoset &p_infoset) const;
   std::optional<T> GetBeliefProb(const GameNode &node) const;
   Vector<T> GetPayoff(const GameNode &node) const;
-  std::optional<T> GetPayoff(const GamePlayer &player, const GameNode &node) const;
+  const T &GetPayoff(const GamePlayer &p_player, const GameNode &p_node) const;
   std::optional<T> GetPayoff(const GameInfoset &p_infoset) const;
   std::optional<T> GetPayoff(const GameAction &act) const;
   T GetActionProb(const GameAction &act) const;

src/pygambit/behavmixed.pxi

@@ -637,13 +637,10 @@ class MixedBehaviorProfile:
         return self._payoff(resolved_player)
 
     def node_value(self, player: PlayerReference,
-                   node: NodeReference) -> ProfileDType | None:
+                   node: NodeReference) -> ProfileDType:
         """Returns the expected payoff to `player` conditional on play reaching `node`,
         if all players play according to the profile.
 
-        If the node's information set is not reachable, in general the node value
-        is not well-defined.  In this case, the function returns `None`.
-
         Parameters
         ----------
         player : Player or str
@@ -663,10 +660,6 @@ class MixedBehaviorProfile:
             `node` is a string and no node in the game has that label.
         ValueError
             If `player` resolves to the chance player
-
-        See Also
-        --------
-        MixedBehaviorProfile.infoset_prob
         """
         self._check_validity()
         resolved_player = self.game._resolve_player(player, "node_value")
@@ -990,11 +983,8 @@ class MixedBehaviorProfileDouble(MixedBehaviorProfile):
             return value.value()
         return None
 
-    def _node_value(self, player: Player, node: Node) -> float | None:
-        cdef optional[double] value = deref(self.profile).GetPayoff(player.player, node.node)
-        if value.has_value():
-            return value.value()
-        return None
+    def _node_value(self, player: Player, node: Node) -> float:
+        return deref(self.profile).GetPayoff(player.player, node.node)
 
     def _action_value(self, action: Action) -> float | None:
         cdef optional[double] value = deref(self.profile).GetPayoff(action.action)
@@ -1104,11 +1094,8 @@ class MixedBehaviorProfileRational(MixedBehaviorProfile):
             return rat_to_py(value.value())
         return None
 
-    def _node_value(self, player: Player, node: Node) -> Rational | None:
-        cdef optional[c_Rational] value = deref(self.profile).GetPayoff(player.player, node.node)
-        if value.has_value():
-            return rat_to_py(value.value())
-        return None
+    def _node_value(self, player: Player, node: Node) -> Rational:
+        return rat_to_py(deref(self.profile).GetPayoff(player.player, node.node))
 
     def _action_value(self, action: Action) -> Rational | None:
         cdef optional[c_Rational] value = deref(self.profile).GetPayoff(action.action)

src/pygambit/gambit.pxd

@@ -367,7 +367,7 @@ cdef extern from "games/behavmixed.h" namespace "Gambit":
         T GetRealizProb(c_GameNode) except +
         T GetInfosetProb(c_GameInfoset) except +
         optional[T] GetPayoff(c_GameInfoset) except +
-        optional[T] GetPayoff(c_GamePlayer, c_GameNode) except +
+        T GetPayoff(c_GamePlayer, c_GameNode) except +
         optional[T] GetPayoff(c_GameAction) except +
         T GetRegret(c_GameAction) except +
         T GetRegret(c_GameInfoset) except +

tests/test_behav.py

@@ -2117,15 +2117,6 @@ def test_undefined_belief():
         assert profile.belief(node) is None
 
 
-def test_undefined_node_value():
-    """Test that undefined node values return `None`."""
-    game = gbt.catalog.load("selten1975/fig1")
-    node = game.players[2].infosets[0].members[0]
-    for rat in [False, True]:
-        profile = game.mixed_behavior_profile([[[1, 0]], [[1, 0]], [[1, 0]]], rational=rat)
-        assert profile.node_value(node.player, node) is None
-
-
 def test_undefined_infoset_value():
     """Test that undefined infoset values return `None`."""
     game = gbt.catalog.load("selten1975/fig1")