updated anticommuting check to be faster and played with commutes_ter…

…mwise sparse (dense method seems fastest for now)

symmer/operators/anticommuting_op.py

@@ -20,8 +20,9 @@ def __init__(self,
  super().__init__(AC_op_symp_matrix, coeff_list)
 
  # check all operators anticommute
- anti_comm_check = self.adjacency_matrix.astype(int) - np.eye(self.adjacency_matrix.shape[0])
- assert (np.sum(anti_comm_check) == 0), 'operator needs to be made of anti-commuting Pauli operators'
+ adj_mat = self.adjacency_matrix
+ adj_mat[np.diag_indices_from(adj_mat)] = False
+ assert ~np.any(adj_mat), 'operator needs to be made of anti-commuting Pauli operators'
 
  self.X_sk_rotations = []
  self.R_LCU = None

symmer/operators/base.py

@@ -975,6 +975,14 @@ def commutes_termwise(self,
  np.array: A Boolean array indicating the term-wise commutation.
  """
  assert (self.n_qubits == PwordOp.n_qubits), 'Pauliwords defined for different number of qubits'
+
+ ### sparse code
+ # adjacency_matrix = (
+ # csr_matrix(self.symp_matrix.astype(int)) @ csr_matrix(np.hstack((PwordOp.Z_block, PwordOp.X_block)).astype(int)).T)
+ # adjacency_matrix.data = ((adjacency_matrix.data % 2) != 0)
+ # return np.logical_not(adjacency_matrix.toarray())
+
+ ### dense code
  Omega_PwordOp_symp = np.hstack((PwordOp.Z_block, PwordOp.X_block)).astype(int)
  return (self.symp_matrix @ Omega_PwordOp_symp.T) % 2 == 0
 
@@ -1089,6 +1097,14 @@ def is_noncontextual(self) -> bool:
  bool: True if the operator is noncontextual, False if contextual.
  """
  # if generators of operator (self) are noncontextual then whole of operator (self) must be too!
+ if self.n_terms<= 2*self.n_qubits+1:
+ # check edge case where all terms are anticommuting
+ adj_mat = self.adjacency_matrix
+ adj_mat[np.diag_indices_from(adj_mat)] = False
+ if ~np.any(adj_mat):
+ # operator is all anticommuting
+ return True
+
  from symmer.utils import get_generators_including_xz_products
  xyz_generators = get_generators_including_xz_products(self)
 

tests/test_operators/test_base.py

@@ -650,6 +650,25 @@ def test_is_noncontextual_generators():
  # assert check_adjmat_noncontextual(Hnc.generators.adjacency_matrix), 'noncontexutal operator is being correctly defined as noncontextual'
  assert Hnc.is_noncontextual, 'noncontexutal operator is being correctly defined as noncontextual'
 
+def test_is_noncontextual_anticommuting_H():
+ """
+ noncontextual test that breaks if only 2n generators are used rather than 3n generators
+ Returns:
+
+ """
+ Hnc = PauliwordOp.from_dictionary({
+ 'ZZZI': (1.2532436410975218-0j),
+ 'IIXI': (0.8935108507410493-0j),
+ 'ZIYI': (-1.1362909076230914+0j),
+ 'IXZI': (-0.05373661687140326+0j),
+ 'ZYZI': (-1.0012312990477774+0j),
+ 'XXYI': (-0.045809456087963205+0j),
+ 'YXYZ': (0.21569499626612557-0j),
+ 'YXYX': (-0.5806963175396661+0j),
+ 'YXYY': (0.3218493853030614-0j)})
+
+ assert Hnc.is_noncontextual, 'noncontexutal operator is being correctly defined as noncontextual'
+
 def test_multiplication_1():
  """ Tests multiplication and the OpenFermion conversion
  """