def test_simplify(self):
"""Test simplify"""
with self.subTest("simplify integer"):
fer_op = FermionicOp("N") + FermionicOp("E") + FermionicOp("N")
simplified_op = fer_op.simplify()
targ = FermionicOp([("N", 2), ("E", 1)])
self.assertFermionEqual(simplified_op, targ)
with self.subTest("simplify complex"):
fer_op = FermionicOp(
"+") + 1j * FermionicOp("-") + 1j * FermionicOp("+")
simplified_op = fer_op.simplify()
targ = FermionicOp([("+", 1 + 1j), ("-", 1j)])
self.assertFermionEqual(simplified_op, targ)
with self.subTest("simplify doesn't reorder"):
fer_op = FermionicOp("+_1 -_0")
simplified_op = fer_op.simplify()
expected = [((("-", 0), ("+", 1)), -1)]
self.assertEqual(simplified_op._data, expected)
with self.subTest("simplify zero"):
fer_op = FermionicOp("+") - FermionicOp("+")
simplified_op = fer_op.simplify()
targ = FermionicOp.zero(1)
self.assertFermionEqual(simplified_op, targ)
def to_second_q_op(self) -> FermionicOp:
"""Creates the operator representing the Hamiltonian defined by these electronic integrals.
This method uses ``to_spin`` internally to map the electronic integrals into the spin
orbital basis.
Returns:
The :class:`~qiskit_nature.second_q.operators.FermionicOp` given by these
electronic integrals.
"""
spin_matrix = self.to_spin()
register_length = len(spin_matrix)
if not np.any(spin_matrix):
return FermionicOp.zero(register_length)
spin_matrix_iter = spin_matrix.flat
# NOTE: we need to access `.coords` before `.next()` is called for the first time!
coords = spin_matrix_iter.coords
op_data = []
for coeff in spin_matrix_iter:
if coeff:
op_data.append((self._calc_coeffs_with_ops(coords), coeff))
coords = spin_matrix_iter.coords
return FermionicOp(op_data, register_length=register_length, display_format="sparse")