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Fixed expectation_computational_basis_state #1194

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Fixed expectation_computational_basis_state #1194

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8 changes: 6 additions & 2 deletions src/openfermion/linalg/sparse_tools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -700,7 +700,7 @@ def expectation_computational_basis_state(operator, computational_basis_state):
If operator is a FermionOperator, it must be normal-ordered.
computational_basis_state (scipy.sparse vector / list): normalized
computational basis state (if scipy.sparse vector), or list of
occupied orbitals.
zeros and ones for occupied and unoccupied orbitals, respectively.

Returns:
A real float giving expectation value.
Expand All @@ -714,6 +714,9 @@ def expectation_computational_basis_state(operator, computational_basis_state):
if not isinstance(operator, FermionOperator):
raise TypeError('operator must be a FermionOperator.')

if not operator.is_normal_ordered():
raise ValueError('operator must be a normal ordered.')

occupied_orbitals = computational_basis_state

if not isinstance(occupied_orbitals, list):
Expand All @@ -730,7 +733,8 @@ def expectation_computational_basis_state(operator, computational_basis_state):
expectation_value += operator.terms.get(((i, 1), (i, 0)), 0.0)

for j in range(i + 1, len(occupied_orbitals)):
expectation_value -= operator.terms.get(((j, 1), (i, 1), (j, 0), (i, 0)), 0.0)
if occupied_orbitals[j]:
expectation_value -= operator.terms.get(((j, 1), (i, 1), (j, 0), (i, 0)), 0.0)

return expectation_value

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11 changes: 11 additions & 0 deletions src/openfermion/linalg/sparse_tools_test.py
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Expand Up @@ -727,6 +727,17 @@ def test_expectation_qubit_operator_not_implemented(self):
QubitOperator(), csc_matrix(([1], ([6], [0])), shape=(16, 1))
)

def test_expectation_bad_operator_order(self):
operator = (
FermionOperator('2^ 2', 1.9)
+ FermionOperator('2^ 1')
+ FermionOperator('2^ 1 2 1^', -1.7)
)
state = [0, 1, 1]

with self.assertRaises(ValueError):
expectation_computational_basis_state(operator, state)


class ExpectationDualBasisOperatorWithPlaneWaveBasisState(unittest.TestCase):
def setUp(self):
Expand Down