probs of actions at chance node normalized after an action is deleted

src/games/game.h

@@ -847,6 +847,8 @@ class GameRep : public BaseGameRep {
   //@{
   /// Set the probability distribution of actions at a chance node
   virtual Game SetChanceProbs(const GameInfoset &, const Array<Number> &) = 0;
+  /// Normalize the probability distribution of actions at a chance node
+  virtual Game NormalizeChanceProbs(const GameInfoset &) = 0;
   //@}
 };
 

src/games/gameagg.h

@@ -147,6 +147,7 @@ class GameAggRep : public GameRep {
   /// @name Modification
   //@{
   Game SetChanceProbs(const GameInfoset &, const Array<Number> &) override { throw UndefinedException(); }
+  Game NormalizeChanceProbs(const GameInfoset &) override { throw UndefinedException(); }
   //@}
 
   /// @name Writing data files

src/games/gamebagg.h

@@ -154,6 +154,7 @@ class GameBagentRep : public GameRep {
   /// @name Modification
   //@{
   Game SetChanceProbs(const GameInfoset &, const Array<Number> &) override { throw UndefinedException(); }
+  Game NormalizeChanceProbs(const GameInfoset &) override { throw UndefinedException(); }
   //@}
 };
 

src/games/gametable.h

@@ -116,6 +116,7 @@ class GameTableRep : public GameExplicitRep {
   /// @name Modification
   //@{
   Game SetChanceProbs(const GameInfoset &, const Array<Number> &) override { throw UndefinedException(); }
+  Game NormalizeChanceProbs(const GameInfoset &) override { throw UndefinedException(); }
   //@}
 
   PureStrategyProfile NewPureStrategyProfile() const override;

src/games/gametree.cc

@@ -62,6 +62,10 @@ void GameTreeActionRep::DeleteAction()
     member->children[where]->DeleteTree();
     member->children.Remove(where)->Invalidate();
   }
+
+  if (m_infoset->IsChanceInfoset()) {
+      m_infoset->m_efg->NormalizeChanceProbs(m_infoset);
+  }
   m_infoset->m_efg->ClearComputedValues();
   m_infoset->m_efg->Canonicalize();
 }
@@ -1054,6 +1058,45 @@ Game GameTreeRep::SetChanceProbs(const GameInfoset &p_infoset, const Array<Numbe
   return this;
 }
 
+Game GameTreeRep::NormalizeChanceProbs(const GameInfoset &m_infoset) {
+    if (m_infoset->GetGame() != this) {
+        throw MismatchException();
+    }
+    if (!m_infoset->IsChanceInfoset()) {
+        throw UndefinedException("Action probabilities can only be normalized for chance information sets");
+    }
+    Rational sum(0);
+    for (int act = 1; act <= m_infoset->NumActions(); act++) {
+        Rational action_prob(m_infoset->GetActionProb(act));
+        std::cout << "action prob BEFORE NORM: " << action_prob << '\n';
+        sum += action_prob;
+    }
+    Array <Number> m_probs(m_infoset->NumActions());
+    std::cout << "COMPUTED SUM IS: " << sum << '\n';
+    if (sum == Rational(0)) {
+        // all remaining moves have prob zero; split prob 1 equally among them
+        for (int act = 1; act <= m_infoset->NumActions(); act++) {
+            std::cout << "SUM 0\n";
+            m_probs[act] = Rational(1, m_infoset->NumActions());
+            std::cout << "action prob SET UNIFORM: " << (std::string) m_probs[act] << '\n';
+        }
+    }
+    else {
+        for (int act = 1; act <= m_infoset->NumActions(); act++) {
+            Rational prob(m_infoset->GetActionProb(act));
+            m_probs[act] = prob / sum;
+            std::cout << "action prob SET NORMALIZE: " << (std::string) m_probs[act] << '\n';
+        }
+    }
+   m_infoset->GetGame()->SetChanceProbs(m_infoset, m_probs);
+
+   for (int act = 1; act <= m_infoset->NumActions(); act++) {
+       Rational prob(m_infoset->GetActionProb(act));
+       std::cout << "action prob NORMALIZED: " << prob << '\n';
+   }
+
+   return this;
+}
 
 //------------------------------------------------------------------------
 //                     GameTreeRep: Factory functions

src/games/gametree.h

@@ -281,6 +281,7 @@ class GameTreeRep : public GameExplicitRep {
   /// @name Modification
   //@{
   Game SetChanceProbs(const GameInfoset &, const Array<Number> &) override;
+  Game NormalizeChanceProbs(const GameInfoset &) override;
   //@}
 
   PureStrategyProfile NewPureStrategyProfile() const override;

src/pygambit/tests/test_actions.py

@@ -96,3 +96,33 @@ def test_action_delete_last(game: gbt.Game):
         game.delete_action(node.infoset.actions[0])
     with pytest.raises(gbt.UndefinedOperationError):
         game.delete_action(node.infoset.actions[0])
+
+
+@pytest.mark.parametrize(
+    "game",
+    [gbt.Game.read_game("test_games/chance_root_3_moves_only_one_nonzero_prob.efg"),]
+)
+# gbt.Game.read_game("test_games/complicated_extensive_game.efg"),
+# gbt.Game.read_game("test_games/chance_root_5_moves_no_nonterm_player_nodes.efg")]
+def test_action_delete_chance(game: gbt.Game):
+    """ """
+    chance_iset = game.players.chance.infosets[0]
+    while len(chance_iset.actions) > 1:
+        check_flag = False
+        if chance_iset.actions[0].prob == 0:
+            print("CHECK FLAG IS TRUE")
+            # the move we are about to delete has 0 prob so nothing should change
+            check_flag = True
+            # keep copy of old probs to check that nothing changed
+            old_probs = [a.prob for a in chance_iset.actions]
+            print("old_probs", old_probs)
+        print("chance_iset.actions[0]).prob", chance_iset.actions[0].prob)
+        game.delete_action(chance_iset.actions[0])
+        # always check that new prob sum is 1
+        assert sum([a.prob for a in chance_iset.actions]) == 1
+        if check_flag:
+            new_probs = [a.prob for a in chance_iset.actions]
+            for p1, p2 in zip(old_probs[1:], new_probs):
+                assert p1 == p2
+    with pytest.raises(gbt.UndefinedOperationError):
+        game.delete_action(chance_iset.actions[0])

src/pygambit/tests/test_games/chance_root_3_moves_only_one_nonzero_prob.efg

@@ -0,0 +1,9 @@
+EFG 2 R "A chance node with 3 moves, 2 with zero prob; one non-terminal player node" { "Player" }
+""
+
+c "" 1 "(0,1)" { "A" 0 "B" 0 "C" 1 } 0 
+p "" 1 1 "(1,1)" { "LEFT" "RIGHT" } 0
+t "" 1 "Outcome 1" { 0 }
+t "" 2 "Outcome 2" { 1 }
+t "" 3 "Outcome 3" { 2 }
+t "" 4 "Outcome 4" { 3 }

src/pygambit/tests/test_games/chance_root_5_moves_no_nonterm_player_nodes.efg

@@ -0,0 +1,9 @@
+EFG 2 R "A chance node with 5 moves; no non-terminal player node" { "Player" }
+""
+
+c "" 1 "" { "A" 1/3 "B" 0 "C" 1/3 "D" 1/3 "E" 0 } 0
+t "" 1 "A" { 0 }
+t "" 2 "B" { 1 }
+t "" 3 "C" { 3 }
+t "" 4 "D" { 3 }
+t "" 5 "E" { 4 }