Return optional for belief

Author: tturocy

src/games/behavmixed.cc

@@ -285,10 +285,14 @@ template <class T> T MixedBehaviorProfile<T>::GetInfosetProb(const GameInfoset &
                       [&](const auto &node) -> T { return m_cache.m_realizProbs[node]; });
 }
 
-template <class T> const T &MixedBehaviorProfile<T>::GetBeliefProb(const GameNode &node) const
+template <class T>
+std::optional<T> MixedBehaviorProfile<T>::GetBeliefProb(const GameNode &node) const
 {
   CheckVersion();
   EnsureBeliefs();
+  if (!node->GetInfoset() || GetInfosetProb(node->GetInfoset()) == T{0}) {
+    return std::nullopt;
+  }
   return m_cache.m_beliefs[node];
 }
 

src/games/behavmixed.h

@@ -241,7 +241,7 @@ template <class T> class MixedBehaviorProfile {
 
   const T &GetRealizProb(const GameNode &node) const;
   T GetInfosetProb(const GameInfoset &p_infoset) const;
-  const T &GetBeliefProb(const GameNode &node) const;
+  std::optional<T> GetBeliefProb(const GameNode &node) const;
   Vector<T> GetPayoff(const GameNode &node) const;
   const T &GetPayoff(const GamePlayer &player, const GameNode &node) const;
   const T &GetPayoff(const GameInfoset &p_infoset) const;

src/gui/analysis.cc

@@ -240,9 +240,9 @@ std::string AnalysisProfileList<T>::GetBeliefProb(const GameNode &p_node, int p_
   }
 
   try {
-    if (m_behavProfiles[index]->GetInfosetProb(p_node->GetInfoset()) > Rational(0)) {
-      return lexical_cast<std::string>(m_behavProfiles[index]->GetBeliefProb(p_node),
-                                       m_doc->GetStyle().NumDecimals());
+    auto belief = m_behavProfiles[index]->GetBeliefProb(p_node);
+    if (belief.has_value()) {
+      return lexical_cast<std::string>(belief.value(), m_doc->GetStyle().NumDecimals());
     }
     // We don't compute assessments yet!
     return "*";

src/pygambit/behavmixed.pxi

@@ -587,10 +587,13 @@ class MixedBehaviorProfile:
         self._check_validity()
         return self._is_defined_at(self.game._resolve_infoset(infoset, "is_defined_at"))
 
-    def belief(self, node: NodeReference) -> ProfileDType:
+    def belief(self, node: NodeReference) -> ProfileDType | None:
         """Returns the conditional probability that a node is reached, given that
         its information set is reached.
 
+        If the information set is not reachable, the belief is not well-defined.
+        In this case, the function returns `None`.
+
         Parameters
         ----------
         node
@@ -952,7 +955,10 @@ class MixedBehaviorProfileDouble(MixedBehaviorProfile):
         return deref(self.profile).GetPayoff(player.player)
 
     def _belief(self, node: Node) -> float:
-        return deref(self.profile).GetBeliefProb(node.node)
+        cdef optional[double] value = deref(self.profile).GetBeliefProb(node.node)
+        if value.has_value():
+            return value.value()
+        return None
 
     def _realiz_prob(self, node: Node) -> float:
         return deref(self.profile).GetRealizProb(node.node)
@@ -967,7 +973,7 @@ class MixedBehaviorProfileDouble(MixedBehaviorProfile):
         return deref(self.profile).GetPayoff(player.player, node.node)
 
     def _action_value(self, action: Action) -> float | None:
-        cdef optional[float] value = deref(self.profile).GetPayoff(action.action)
+        cdef optional[double] value = deref(self.profile).GetPayoff(action.action)
         if value.has_value():
             return value.value()
         return None
@@ -1057,7 +1063,10 @@ class MixedBehaviorProfileRational(MixedBehaviorProfile):
         return rat_to_py(deref(self.profile).GetPayoff(player.player))
 
     def _belief(self, node: Node) -> Rational:
-        return rat_to_py(deref(self.profile).GetBeliefProb(node.node))
+        cdef optional[c_Rational] value = deref(self.profile).GetBeliefProb(node.node)
+        if value.has_value():
+            return rat_to_py(value.value())
+        return None
 
     def _realiz_prob(self, node: Node) -> Rational:
         return rat_to_py(deref(self.profile).GetRealizProb(node.node))

src/pygambit/gambit.pxd

@@ -363,7 +363,7 @@ cdef extern from "games/behavmixed.h" namespace "Gambit":
         T getitem "operator[]"(int) except +IndexError
         T getaction "operator[]"(c_GameAction) except +IndexError
         T GetPayoff(c_GamePlayer) except +
-        T GetBeliefProb(c_GameNode) except +
+        optional[T] GetBeliefProb(c_GameNode) except +
         T GetRealizProb(c_GameNode) except +
         T GetInfosetProb(c_GameInfoset) except +
         T GetPayoff(c_GameInfoset) except +

src/tools/util.h

@@ -256,7 +256,13 @@ void MixedBehaviorProfileDetailRenderer<T>::Render(const MixedBehaviorProfile<T>
           m_stream << std::setw(7) << node->GetNumber() << "   ";
         }
         m_stream << std::setw(11);
-        m_stream << lexical_cast<std::string>(p_profile.GetBeliefProb(node), m_numDecimals);
+        auto belief = p_profile.GetBeliefProb(node);
+        if (belief.has_value()) {
+          m_stream << lexical_cast<std::string>(belief.value(), m_numDecimals);
+        }
+        else {
+          m_stream << "";
+        }
         m_stream << "   ";
         m_stream << std::setw(11);
         m_stream << lexical_cast<std::string>(p_profile.GetRealizProb(node), m_numDecimals);

tests/test_behav.py

@@ -2106,3 +2106,12 @@ def test_undefined_action_value():
     for rat in [False, True]:
         profile = game.mixed_behavior_profile([[[1, 0]], [[1, 0]], [[1, 0]]], rational=rat)
         assert profile.action_value(action) is None
+
+
+def test_undefined_belief():
+    """Test that undefined beliefs 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.belief(node) is None