copy _grounds in clone() and use other.is_ground(v) in tensor()

CHANGELOG.md

@@ -17,6 +17,7 @@ Hence, occasionally changes will be backwards incompatible (although they will a
 - Incorrect scalar in the Z-X bialgebra rule when both spiders carry Pauli phases, including symbolic Boolean phases (by @dlyongemallo).
 - `subgraph_from_vertices` copies only variables used in the subgraph (by @dlyongemallo).
 - `extract_circuit` raises `ValueError` for graphs containing ground vertices or mismatched input/output counts, instead of a `KeyError` crash (by @dlyongemallo).
+- Missed copying `_grounds` in `clone()`, incorrectly checking destination `is_ground` instead of source in `tensor()` (by @dlyongemallo).
 
 ### Changed
 - Migrated project configuration from `setup.py` to `pyproject.toml`. Make the `galois` package an optional dependency, as it is only used in `pyzx.web`. (by @dlyongemallo)

pyzx/graph/base.py

@@ -620,7 +620,7 @@ def tensor(self, other: BaseGraph[VT,ET]) -> BaseGraph[VT,ET]:
         phases = other.phases()
         vertex_map = dict()
         for v in other.vertices():
-            w = g.add_vertex(ts[v],qs[v]+height,rs[v],phases[v],g.is_ground(v))
+            w = g.add_vertex(ts[v],qs[v]+height,rs[v],phases[v],other.is_ground(v))
             g.set_vdata_dict(w, other.vdata_dict(v))
             vertex_map[v] = w
         for e in other.edges():

pyzx/graph/graph_s.py

@@ -59,6 +59,7 @@ def clone(self) -> 'GraphS':
         cpy._maxr = self._maxr
         cpy._vdata = self._vdata.copy()
         cpy.scalar = self.scalar.copy()
+        cpy._grounds = self._grounds.copy()
         cpy._inputs = tuple(list(self._inputs))
         cpy._outputs = tuple(list(self._outputs))
         cpy.track_phases = self.track_phases

pyzx/graph/multigraph.py

@@ -97,6 +97,7 @@ def clone(self) -> 'Multigraph':
         cpy._vdata = self._vdata.copy()
         cpy._edata = {k: v.copy() for k, v in self._edata.items()}
         cpy.scalar = self.scalar.copy()
+        cpy._grounds = self._grounds.copy()
         cpy._inputs = tuple(list(self._inputs))
         cpy._outputs = tuple(list(self._outputs))
         cpy.track_phases = self.track_phases

tests/test_graph.py

@@ -160,6 +160,31 @@ def test_copy(self):
         v1, v2 = list(g2.vertices())
         self.assertEqual(g.edge_type(g.edge(v1,v2)),EdgeType.HADAMARD)
 
+    def test_clone_grounds(self):
+        """clone() should preserve ground status of vertices."""
+        for backend in ["simple", "multigraph"]:
+            with self.subTest(backend=backend):
+                g = Graph(backend=backend)
+                v1 = g.add_vertex(VertexType.Z, 0, 0)
+                v2 = g.add_vertex(VertexType.Z, 0, 1, ground=True)
+                g.add_edge((v1, v2))
+                g2 = g.clone()
+                self.assertTrue(g2.is_ground(v2))
+                self.assertFalse(g2.is_ground(v1))
+
+    def test_tensor_grounds(self):
+        """tensor() should preserve grounds from the other graph."""
+        for backend in ["simple", "multigraph"]:
+            with self.subTest(backend=backend):
+                g1 = Graph(backend=backend)
+                g1.add_vertex(VertexType.Z, 0, 0)
+
+                g2 = Graph(backend=backend)
+                g2.add_vertex(VertexType.Z, 0, 0, ground=True)
+
+                g = g1.tensor(g2)
+                self.assertEqual(len(g.grounds()), 1)
+
     def test_adjoint_scalar(self):
         g = Graph()
         scalar = Scalar()