def _add(self, other):
"""Return the operator self + other.
Args:
other (BaseOperator): an operator object.
Returns:
ScalarOp: if other is an ScalarOp.
BaseOperator: if other is not an ScalarOp.
Raises:
QiskitError: if other has incompatible dimensions.
"""
if not isinstance(other, BaseOperator):
other = Operator(other)
self._validate_add_dims(other)
# First we check the special case where coeff=0. In this case
# we simply return the other operator reshaped so that its
# subsystem dimensions are equal to the current operator for the
# case where total dimensions agree but subsystem dimensions differ.
if self.coeff == 0:
return other.reshape(self._input_dims, self._output_dims)
# Next if we are adding two ScalarOps we return a ScalarOp
if isinstance(other, ScalarOp):
coeff1 = 1 if self.coeff is None else self.coeff
coeff2 = 1 if other.coeff is None else other.coeff
return ScalarOp(self._input_dims, coeff=coeff1 + coeff2)
# Finally if we are adding another BaseOperator subclass
# we use that subclasses `_add` method and reshape the
# final dimensions.
return other._add(self).reshape(self._input_dims, self._output_dims)
def test_add(self):
"""Test add method."""
mat1 = self.rand_matrix(4, 4)
mat2 = self.rand_matrix(4, 4)
op1 = Operator(mat1)
op2 = Operator(mat2)
self.assertEqual(op1._add(op2), Operator(mat1 + mat2))
self.assertEqual(op1 + op2, Operator(mat1 + mat2))
self.assertEqual(op1 - op2, Operator(mat1 - mat2))
