From 63da24b0962763ebecc7e3fa7112b0a0693ddd5c Mon Sep 17 00:00:00 2001
From: Julien Gacon <jules.gacon@googlemail.com>
Date: Tue, 5 Nov 2024 21:30:54 +0100
Subject: [PATCH] Fix CC for comparison with rotation gates on angles k*pi

---
 crates/accelerate/src/commutation_checker.rs  |  4 +-
 .../circuit/test_commutation_checker.py       | 54 +++++++++++++------
 2 files changed, 42 insertions(+), 16 deletions(-)

diff --git a/crates/accelerate/src/commutation_checker.rs b/crates/accelerate/src/commutation_checker.rs
index 16fcc5eca8fb..fe242c73422f 100644
--- a/crates/accelerate/src/commutation_checker.rs
+++ b/crates/accelerate/src/commutation_checker.rs
@@ -43,6 +43,8 @@ static SUPPORTED_OP: Lazy<HashSet<&str>> = Lazy::new(|| {
     ])
 });
 
+const TWOPI: f64 = 2.0 * std::f64::consts::PI;
+
 // map rotation gates to their generators, or to ``None`` if we cannot currently efficiently
 // represent the generator in Rust and store the commutation relation in the commutation dictionary
 static SUPPORTED_ROTATIONS: Lazy<HashMap<&str, Option<OperationRef>>> = Lazy::new(|| {
@@ -632,7 +634,7 @@ fn map_rotation<'a>(
         // commute with everything, and we simply return the operation with the flag that
         // it commutes trivially
         if let Param::Float(angle) = params[0] {
-            if (angle % std::f64::consts::PI).abs() < tol {
+            if (angle % TWOPI).abs() < tol {
                 return (op, params, true);
             };
         };
diff --git a/test/python/circuit/test_commutation_checker.py b/test/python/circuit/test_commutation_checker.py
index 8bb3f6939add..9759b5bffd1e 100644
--- a/test/python/circuit/test_commutation_checker.py
+++ b/test/python/circuit/test_commutation_checker.py
@@ -16,7 +16,7 @@
 from test import QiskitTestCase  # pylint: disable=wrong-import-order
 
 import numpy as np
-from ddt import data, ddt
+from ddt import idata, ddt
 
 from qiskit import ClassicalRegister
 from qiskit.circuit import (
@@ -52,9 +52,25 @@
     SGate,
     XGate,
     ZGate,
+    HGate,
 )
 from qiskit.dagcircuit import DAGOpNode
 
+ROTATION_GATES = [
+    RXGate,
+    RYGate,
+    RZGate,
+    PhaseGate,
+    CRXGate,
+    CRYGate,
+    CRZGate,
+    CPhaseGate,
+    RXXGate,
+    RYYGate,
+    RZZGate,
+    RZXGate,
+]
+
 
 class NewGateCX(Gate):
     """A dummy class containing an cx gate unknown to the commutation checker's library."""
@@ -373,20 +389,7 @@ def test_serialization(self):
         cc2.commute_nodes(dop1, dop2)
         self.assertEqual(cc2.num_cached_entries(), 1)
 
-    @data(
-        RXGate,
-        RYGate,
-        RZGate,
-        PhaseGate,
-        CRXGate,
-        CRYGate,
-        CRZGate,
-        CPhaseGate,
-        RXXGate,
-        RYYGate,
-        RZZGate,
-        RZXGate,
-    )
+    @idata(ROTATION_GATES)
     def test_cutoff_angles(self, gate_cls):
         """Check rotations with a small enough angle are cut off."""
         max_power = 30
@@ -406,6 +409,27 @@ def test_cutoff_angles(self, gate_cls):
             else:
                 self.assertFalse(scc.commute(generic_gate, [0, 1], [], gate, qargs, []))
 
+    @idata(ROTATION_GATES)
+    def test_rotation_mod_2pi(self, gate_cls):
+        """Test the rotations modulo 2pi commute with any gate."""
+        generic_gate = HGate()  # does not commute with any rotation gate
+        even = np.arange(-6, 7, 2)
+
+        with self.subTest(msg="even multiples"):
+            for multiple in even:
+                gate = gate_cls(multiple * np.pi)
+                self.assertTrue(
+                    scc.commute(generic_gate, [0], [], gate, list(range(gate.num_qubits)), [])
+                )
+
+        odd = np.arange(-5, 6, 2)
+        with self.subTest(msg="odd multiples"):
+            for multiple in odd:
+                gate = gate_cls(multiple * np.pi)
+                self.assertFalse(
+                    scc.commute(generic_gate, [0], [], gate, list(range(gate.num_qubits)), [])
+                )
+
 
 if __name__ == "__main__":
     unittest.main()