add is_cluster_neutral

src/qiskit_qec/circuits/bindings/circuits_bindings.cpp

@@ -8,4 +8,5 @@ PYBIND11_MODULE(_c_circuits, module)
 {
   module.doc() = "qiskit-qec code circuit extensions";
   module.def("_c_check_nodes", &check_nodes, "check_nodes in C++");
+  module.def("_c_is_cluster_neutral", &is_cluster_neutral, "is_cluster_neutral in C++");
 }

src/qiskit_qec/circuits/intern/arctools.cpp

@@ -1,5 +1,19 @@
 #include "arctools.h"
 
+bool is_cluster_neutral(
+    std::vector<std::tuple<int, int, int, bool>> nodes, bool ignore_extra_logicals, bool minimal,
+    std::map<std::tuple<int, int>, std::set<int>> cycle_dict, std::vector<std::tuple<int, int>> link_graph, std::map<int, std::vector<int>> link_neighbors, std::vector<int> z_logicals,
+    bool linear
+    ) {
+    if (linear) {
+        return nodes.size()%2==0;
+    } else {
+        std::vector<int> output = check_nodes(nodes, ignore_extra_logicals, minimal, cycle_dict, link_graph, link_neighbors, z_logicals);
+        return (output[0]==1) and (output.size()==0);
+    }
+
+};
+
 std::vector<int> check_nodes(
     std::vector<std::tuple<int, int, int, bool>> nodes, bool ignore_extra_logicals, bool minimal,
     std::map<std::tuple<int, int>, std::set<int>> cycle_dict, std::vector<std::tuple<int, int>> link_graph, std::map<int, std::vector<int>> link_neighbors, std::vector<int> z_logicals

src/qiskit_qec/circuits/repetition_code.py

@@ -32,7 +32,7 @@
 from qiskit_qec.circuits.code_circuit import CodeCircuit
 from qiskit_qec.utils import DecodingGraphEdge, DecodingGraphNode
 from qiskit_qec.utils.decoding_graph_attributes import _nodes2cpp
-from qiskit_qec.circuits._c_circuits import _c_check_nodes
+from qiskit_qec.circuits._c_circuits import _c_check_nodes, _c_is_cluster_neutral
 
 
 def _separate_string(string):
@@ -1367,11 +1367,24 @@ def is_cluster_neutral(self, atypical_nodes: dict, cpp=False):
             atypical_nodes: dictionary in the form of the return value of string2nodes
             cpp (bool): Whether to use C++ implementation.
         """
-        if self._linear:
-            return not bool(len(atypical_nodes) % 2)
+        if cpp:
+            nodes = _nodes2cpp(nodes)
+            return _c_is_cluster_neutral(
+                nodes,
+                False,
+                False,
+                self.cycle_dict,
+                self._cpp_link_graph,
+                self._cpp_link_neighbors,
+                self.z_logicals,
+                self._linear,
+            )
         else:
-            neutral, logicals, _ = self.check_nodes(atypical_nodes, cpp=cpp)
-            return neutral and not logicals
+            if self._linear:
+                return not bool(len(atypical_nodes) % 2)
+            else:
+                neutral, logicals, _ = self.check_nodes(atypical_nodes)
+                return neutral and not logicals
 
     def transpile(self, backend, echo=("X", "X"), echo_num=(2, 0)):
         """