Merge pull request #244 from boldar99/fix-multigraph-rewrites

Fix color_change, fusion, and match_ids

pyzx/basicrules.py

@@ -49,23 +49,18 @@
 from .graph.base import BaseGraph, VT, ET
 from .rules import apply_rule, w_fusion, z_to_z_box
 from .utils import (EdgeType, VertexType, get_w_io, get_z_box_label, is_pauli,
-                    set_z_box_label, vertex_is_w, vertex_is_z_like)
+                    set_z_box_label, vertex_is_w, vertex_is_z_like, toggle_vertex, toggle_edge)
 
 def color_change_diagram(g: BaseGraph[VT,ET]):
     """Color-change an entire diagram by applying Hadamards to the inputs and ouputs."""
     for v in g.vertices():
         if g.type(v) == VertexType.BOUNDARY:
             if g.vertex_degree(v) != 1:
                 raise ValueError("Boundary should only have 1 neighbor.")
-            v1 = next(iter(g.neighbors(v)))
-            e = g.edge(v,v1)
-            g.set_edge_type(e, EdgeType.SIMPLE
-                    if g.edge_type(e) == EdgeType.HADAMARD
-                    else EdgeType.HADAMARD)
-        elif g.type(v) == VertexType.Z:
-            g.set_type(v, VertexType.X)
-        elif g.type(v) == VertexType.X:
-            g.set_type(v, VertexType.Z)
+            for e in g.incident_edges(v):
+                g.set_edge_type(e, toggle_edge(g.edge_type(e)))
+        elif check_color_change(g, v):
+            color_change(g, v)
 
 def check_color_change(g: BaseGraph[VT,ET], v: VT) -> bool:
     if not (g.type(v) == VertexType.Z or g.type(v) == VertexType.X):
@@ -77,12 +72,9 @@ def color_change(g: BaseGraph[VT,ET], v: VT) -> bool:
     if not (g.type(v) == VertexType.Z or g.type(v) == VertexType.X):
         return False
 
-    g.set_type(v, VertexType.Z if g.type(v) == VertexType.X else VertexType.X)
-    for v1 in g.neighbors(v):
-        e = g.edge(v,v1)
-        g.set_edge_type(e, EdgeType.SIMPLE
-                if g.edge_type(e) == EdgeType.HADAMARD
-                else EdgeType.HADAMARD)
+    g.set_type(v, toggle_vertex(g.type(v)))
+    for e in g.incident_edges(v):
+        g.set_edge_type(e, toggle_edge(g.edge_type(e)))
 
     return True
 
@@ -196,7 +188,7 @@ def check_fuse(g: BaseGraph[VT,ET], v1: VT, v2: VT) -> bool:
     if not (g.connected(v1,v2) and
             ((g.type(v1) == VertexType.X and g.type(v2) == VertexType.X) or
              (vertex_is_z_like(g.type(v1)) and vertex_is_z_like(g.type(v2)))) and
-            g.edge_type(g.edge(v1,v2)) == EdgeType.SIMPLE):
+            EdgeType.SIMPLE in [g.edge_type(edge) for edge in g.edges(v1,v2)]):
         return False
     return True
 
@@ -212,9 +204,18 @@ def fuse(g: BaseGraph[VT,ET], v1: VT, v2: VT) -> bool:
         set_z_box_label(g, v1, get_z_box_label(g, v1) * get_z_box_label(g, v2))
     else:
         g.add_to_phase(v1, g.phase(v2))
-    for v3 in g.neighbors(v2):
-        if v3 != v1:
-            g.add_edge((v1,v3), edgetype=g.edge_type(g.edge(v2,v3)))
+    for e in g.incident_edges(v2):
+        source, target = g.edge_st(e)
+        other_vertex = source if source != v2 else target
+        if source != v2:
+            other_vertex = source
+        elif target != v2:
+            other_vertex = target
+        else: #self-loop
+            other_vertex = v1
+        if other_vertex == v1 and g.edge_type(e) == EdgeType.SIMPLE:
+            continue
+        g.add_edge((v1,other_vertex), edgetype=g.edge_type(e))
     g.remove_vertex(v2)
     return True
 

pyzx/editor_actions.py

@@ -53,8 +53,7 @@ def color_change(g: BaseGraph[VT,ET], matches: List[VT]) -> rules.RewriteOutputT
     for v in matches:
         g.set_type(v, toggle_vertex(g.type(v)))
         for e in g.incident_edges(v):
-            et = g.edge_type(e)
-            g.set_edge_type(e, toggle_edge(et))
+            g.set_edge_type(e, toggle_edge(g.edge_type(e)))
     return ({}, [],[],False)
 
 

pyzx/graph/graph_s.py

@@ -217,10 +217,16 @@ def vertices_in_range(self, start, end):
             if all(start<v2<end for v2 in self.graph[v]):
                 yield v
 
-    def edges(self):
-        for v0,adj in self.graph.items():
-            for v1 in adj:
-                if v1 > v0: yield (v0,v1)
+    def edges(self, s=None, t=None):
+        if s is not None and t is not None:
+                yield (s,t) if s < t else (t,s)
+        elif s is not None:
+            for t in self.graph[s]:
+                yield (s,t) if s < t else (t,s)
+        else:
+            for v0,adj in self.graph.items():
+                for v1 in adj:
+                    if v1 > v0: yield (v0,v1)
 
     def edges_in_range(self, start, end, safe=False):
         """like self.edges, but only returns edges that belong to vertices

pyzx/graph/multigraph.py

@@ -14,6 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import itertools
 from collections import Counter
 from fractions import Fraction
 from typing import Tuple, Dict, Set, Any
@@ -323,7 +324,9 @@ def vertex_degree(self, vertex):
         return d
 
     def incident_edges(self, vertex):
-        return [(vertex, v1) if v1 > vertex else (v1, vertex) for v1 in self.graph[vertex]]
+        return list(itertools.chain.from_iterable(
+            self.edges(vertex, v1) for v1 in self.graph[vertex]
+        ))
 
     def connected(self,v1,v2):
         return v2 in self.graph[v1]

pyzx/rules.py

@@ -168,6 +168,7 @@ def match_spider_parallel(
     """
     if matchf is not None: candidates = set([e for e in g.edges() if matchf(e)])
     else: candidates = g.edge_set()
+    candidates = set(candidates)
     types = g.types()
 
     i = 0
@@ -176,6 +177,7 @@ def match_spider_parallel(
         e = candidates.pop()
         if g.edge_type(e) != EdgeType.SIMPLE: continue
         v0, v1 = g.edge_st(e)
+        if v0 == v1: continue
         v0t = types[v0]
         v1t = types[v1]
         if (v0t == v1t and vertex_is_zx(v0t)) or \
@@ -223,11 +225,18 @@ def spider(g: BaseGraph[VT,ET], matches: List[MatchSpiderType[VT]]) -> RewriteOu
         rem_verts.append(v1)
 
         # edges from the second vertex are transferred to the first
-        for w in g.neighbors(v1):
-            if v0 == w: continue
-            e = (v0,w)
-            if e not in etab: etab[e] = [0,0]
-            etab[e][g.edge_type(g.edge(v1,w)) - 1] += 1
+        for e in g.incident_edges(v1):
+            source, target = g.edge_st(e)
+            if source != v1:
+                other_vertex = source
+            elif target != v1:
+                other_vertex = target
+            else: #self-loop
+                other_vertex = v0
+            new_e = (v0, other_vertex)
+            if new_e not in etab: etab[new_e] = [0,0]
+            etab[new_e][g.edge_type(e)-1] += 1
+        etab[(v0,v0)][0] = 0 # remove simple edge loops
     return (etab, rem_verts, [], True)
 
 def unspider(g: BaseGraph[VT,ET], m: List[Any], qubit:FloatInt=-1, row:FloatInt=-1) -> VT:
@@ -780,7 +789,7 @@ def match_ids_parallel(
 
     while (num == -1 or i < num) and len(candidates) > 0:
         v = candidates.pop()
-        if phases[v] != 0 or not vertex_is_zx(types[v]) or g.is_ground(v):
+        if phases[v] != 0 or not vertex_is_zx(types[v]) or g.is_ground(v) or g.vertex_degree(v) != 2:
             continue
         neigh = g.neighbors(v)
         if len(neigh) != 2: continue