Workaround is_isormorphic returning false for 2 empty graphs (#422)

* Workaround is_isormorphic returning false for 2 empty graphs This commit works around the bug in the vf2 implementation for empty graphs where no mapping is found for is_isomorphic. It's just a workaround for the issue reported in #421 and I'm sure there is a better real fix, but in the interest of having a solution proposed in the short term this was fast. Fixes #421 * Bump versions and prepare for release * Update src/isomorphism/vf2.rs Co-authored-by: Ivan Carvalho <[email protected]> * Add subgraph isomorphic tests too
Qiskit · Aug 25, 2021 · b97bc14 · b97bc14
1 parent a71e5bf
commit b97bc14
Show file tree

Hide file tree

Showing 9 changed files with 133 additions and 3 deletions.
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "retworkx"
 description = "A python graph library implemented in Rust"
-version = "0.10.0"
+version = "0.10.1"
 authors = ["Matthew Treinish <[email protected]>"]
 license = "Apache-2.0"
 readme = "README.md"

diff --git a/releasenotes/notes/0.10.0/fix-empty-isomorphism-ccea235b81119b20.yaml b/releasenotes/notes/0.10.0/fix-empty-isomorphism-ccea235b81119b20.yaml
@@ -0,0 +1,5 @@
+---
+prelude: >
+  This is a bugfix release that fixes a regression introduced in the previous
+  0.10.0 release. In 0.10.0 the :func:`~retworkx.is_isomorphic` function when
+  comparing 2 empty graph objects would incorrectly return ``False``.
diff --git a/setup.py b/setup.py
@@ -21,7 +21,7 @@ def readme():
 
 setup(
     name="retworkx",
-    version="0.10.0",
+    version="0.10.1",
     description="A python graph library implemented in Rust",
     long_description=readme(),
     long_description_content_type='text/markdown',

diff --git a/src/isomorphism/vf2.rs b/src/isomorphism/vf2.rs
@@ -375,6 +375,12 @@ pub fn is_isomorphic<Ty: EdgeType>(
     {
         return Ok(false);
     }
+    // TODO: Remove this. This is just a hacky workaround to fix #421 fast,
+    // we should fix VF2Algorithm.next() to return an empty hashmap for
+    // 2 empty graphs
+    if g1.node_count() == 0 && g1.edge_count() == 0 {
+        return Ok(true);
+    }
 
     let mut vf2 = Vf2Algorithm::new(
         py, g0, g1, node_match, edge_match, id_order, ordering, induced,

diff --git a/tests/digraph/test_isomorphic.py b/tests/digraph/test_isomorphic.py
@@ -17,6 +17,38 @@
 
 
 class TestIsomorphic(unittest.TestCase):
+    def test_empty_isomorphic_identical(self):
+        dag_a = retworkx.PyDAG()
+        dag_b = retworkx.PyDAG()
+
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_isomorphic(dag_a, dag_b, id_order=id_order)
+                )
+
+    def test_empty_isomorphic_mismatch_node_data(self):
+        dag_a = retworkx.PyDAG()
+        dag_b = retworkx.PyDAG()
+
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_isomorphic(dag_a, dag_b, id_order=id_order)
+                )
+
+    def test_empty_isomorphic_compare_nodes_mismatch_node_data(self):
+        dag_a = retworkx.PyDAG()
+        dag_b = retworkx.PyDAG()
+
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_isomorphic(
+                        dag_a, dag_b, lambda x, y: x == y, id_order=id_order
+                    )
+                )
+
     def test_isomorphic_identical(self):
         dag_a = retworkx.PyDAG()
         dag_b = retworkx.PyDAG()

diff --git a/tests/digraph/test_subgraph_isomorphic.py b/tests/digraph/test_subgraph_isomorphic.py
@@ -16,6 +16,34 @@
 
 
 class TestSubgraphIsomorphic(unittest.TestCase):
+    def test_empty_subgraph_isomorphic_identical(self):
+        g_a = retworkx.PyDiGraph()
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_subgraph_isomorphic(g_a, g_a, id_order=id_order)
+                )
+
+    def test_empty_subgraph_isomorphic_mismatch_node_data(self):
+        g_a = retworkx.PyDiGraph()
+        g_b = retworkx.PyDiGraph()
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_subgraph_isomorphic(g_a, g_b, id_order=id_order)
+                )
+
+    def test_empty_subgraph_isomorphic_compare_nodes_mismatch_node_data(self):
+        g_a = retworkx.PyDiGraph()
+        g_b = retworkx.PyDiGraph()
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_subgraph_isomorphic(
+                        g_a, g_b, lambda x, y: x == y, id_order=id_order
+                    )
+                )
+
     def test_subgraph_isomorphic_identical(self):
         g_a = retworkx.PyDiGraph()
         nodes = g_a.add_nodes_from(["a_1", "a_2", "a_3"])

diff --git a/tests/graph/test_isomorphic.py b/tests/graph/test_isomorphic.py
@@ -16,6 +16,35 @@
 
 
 class TestIsomorphic(unittest.TestCase):
+    def test_empty_isomorphic_identical(self):
+        g_a = retworkx.PyGraph()
+        g_b = retworkx.PyGraph()
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_isomorphic(g_a, g_b, id_order=id_order)
+                )
+
+    def test_empty_isomorphic_mismatch_node_data(self):
+        g_a = retworkx.PyGraph()
+        g_b = retworkx.PyGraph()
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_isomorphic(g_a, g_b, id_order=id_order)
+                )
+
+    def test_empty_isomorphic_compare_nodes_mismatch_node_data(self):
+        g_a = retworkx.PyGraph()
+        g_b = retworkx.PyGraph()
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_isomorphic(
+                        g_a, g_b, lambda x, y: x == y, id_order=id_order
+                    )
+                )
+
     def test_isomorphic_identical(self):
         g_a = retworkx.PyGraph()
         g_b = retworkx.PyGraph()

diff --git a/tests/graph/test_subgraph_isomorphic.py b/tests/graph/test_subgraph_isomorphic.py
@@ -16,6 +16,34 @@
 
 
 class TestSubgraphIsomorphic(unittest.TestCase):
+    def test_empty_subgraph_isomorphic_identical(self):
+        g_a = retworkx.PyGraph()
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_subgraph_isomorphic(g_a, g_a, id_order=id_order)
+                )
+
+    def test_empty_subgraph_isomorphic_mismatch_node_data(self):
+        g_a = retworkx.PyGraph()
+        g_b = retworkx.PyGraph()
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_subgraph_isomorphic(g_a, g_b, id_order=id_order)
+                )
+
+    def test_empty_subgraph_isomorphic_compare_nodes_mismatch_node_data(self):
+        g_a = retworkx.PyGraph()
+        g_b = retworkx.PyGraph()
+        for id_order in [False, True]:
+            with self.subTest(id_order=id_order):
+                self.assertTrue(
+                    retworkx.is_subgraph_isomorphic(
+                        g_a, g_b, lambda x, y: x == y, id_order=id_order
+                    )
+                )
+
     def test_subgraph_isomorphic_identical(self):
         g_a = retworkx.PyGraph()
         nodes = g_a.add_nodes_from(["a_1", "a_2", "a_3"])