From e9baa88c70a1721636b8842860fe0b4b1a3eda48 Mon Sep 17 00:00:00 2001
From: Joris van Rantwijk <joris@jorisvr.nl>
Date: Sun, 9 Jun 2024 19:49:02 +0200
Subject: [PATCH] Fix bug in delta2 tracking

---
 python/mwmatching.py      |  6 ++++++
 python/test_mwmatching.py | 12 ++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/python/mwmatching.py b/python/mwmatching.py
index 787df39..4d33824 100644
--- a/python/mwmatching.py
+++ b/python/mwmatching.py
@@ -1051,6 +1051,7 @@ class _MatchingContext:
 
         assert blossom.parent is None
         assert blossom.label == _LABEL_T
+        assert blossom.delta2_node is None
 
         # Remove expanded blossom from the delta4 queue.
         assert blossom.delta4_node is not None
@@ -1131,6 +1132,11 @@ class _MatchingContext:
         assert blossom.parent is None
         assert blossom.label == _LABEL_NONE
 
+        # Remove blossom from delta2 heap.
+        assert blossom.delta2_node is not None
+        self.delta2_queue.delete(blossom.delta2_node)
+        blossom.delta2_node = None
+
         # Split union-find structure.
         blossom.vertex_set.split()
 
diff --git a/python/test_mwmatching.py b/python/test_mwmatching.py
index c106c10..05a3a68 100644
--- a/python/test_mwmatching.py
+++ b/python/test_mwmatching.py
@@ -243,6 +243,18 @@ class TestMaximumWeightMatching(unittest.TestCase):
             mwm([(1,2,19), (1,4,17), (1,5,19), (2,3,15), (2,5,21), (4,6,18), (4,7,11), (5,6,19)]),
             [(1,5), (2,3), (4,6)])
 
+    def test61_triangles_n9(self):
+        """t.f 9 nodes"""
+        #
+        #  [1]------[4]      [7]
+        #   | \      | \      | \
+        #   |  [3]   |  [6]   |  [9]
+        #   | /      | /      | /
+        #  [2]      [5]------[8]
+        #
+        result = mwm([(1,2,1), (1,3,1), (2,3,1), (4,5,1), (4,6,1), (5,6,1), (7,8,1), (7,9,1), (8,9,1), (1,4,1), (5,8,1)])
+        self.assertEqual(len(result), 4)
+
     def test_fail_bad_input(self):
         """bad input values"""
         with self.assertRaises(TypeError):