Error in Operator() addition/subtraction in- and out-of-place

[juanjosegarciaripoll]

Informations

• Qiskit Aqua version: 0.5.2
• Python version: 3.6.7
• Operating system: Windows 10 (Miniconda3)

What is the current behavior?

When adding or subtracting Operator() objects, the output is not the result of the operation, but the original operator.

Steps to reproduce the problem

from qiskit.quantum_info import Pauli
from qiskit.aqua import Operator
import copy
aux = Operator(paulis=[(1.0,Pauli(label='II'))])
aux.to_matrix()
print('op1=',aux.matrix)
aux2 = Operator(paulis=[(1.0,Pauli(label='ZI'))])
aux2.to_matrix()
print('op2=',aux2.matrix)

print('---Out-of-place subtraction')
print(aux.matrix-aux2.matrix)
aux3 = aux - aux2
print(aux3.matrix)

print('---Out-of-place addition')
print(aux.matrix+aux2.matrix)
aux3 = aux + aux2
print(aux3.matrix)

print('---In-place subtraction')
aux3 = copy.deepcopy(aux)
print(aux3.matrix)
print(aux.matrix-aux2.matrix)
aux3 -= aux2
print(aux3.matrix)

print('---In-place addition')
aux3 = copy.deepcopy(aux)
print(aux3.matrix)
print(aux3.matrix+aux2.matrix)
aux3 += aux2
print(aux3.matrix)

Output
op1= [1. 1. 1. 1.]
op2= [ 1. 1. -1. -1.]
---Out-of-place subtraction
[0. 0. 2. 2.]
[1. 1. 1. 1.]
---Out-of-place addition
[2. 2. 0. 0.]
[1. 1. 1. 1.]
---In-place subtraction
[1. 1. 1. 1.]
[0. 0. 2. 2.]
[1. 1. 1. 1.]
---In-place addition
[1. 1. 1. 1.]
[2. 2. 0. 0.]
[1. 1. 1. 1.]

What is the expected behavior?

The expected solution is that the third row of each example should be equal to the second row.

Suggested solutions

Fix the Operator() method auxiliary function _extend_or_combine()

[juanjosegarciaripoll]

The following patch fixed the bug

diff --git a/qiskit/aqua/operator.py b/qiskit/aqua/operator.py
index ba315389..8caf7116 100644
--- a/qiskit/aqua/operator.py
+++ b/qiskit/aqua/operator.py
@@ -106,6 +106,7 @@ class Operator(object):
             lhs._paulis_to_grouped_paulis()
         elif lhs._matrix is not None and rhs._matrix is not None:
             lhs._matrix = operation(lhs._matrix, rhs._matrix)
+            lhs._to_dia_matrix(mode="matrix")
         else:
             raise TypeError("the representations of two Operators should be the same. ({}, {})".format(
                 lhs.representations, rhs.representations))

[chunfuchen]

the above patch only fixes for matrix mode. for the pauli mode, another patch is needed (since the right operand is manipulated accidentally.
addressed in #620 and #619

[chunfuchen]

resolved by #620 and #619.

[chunfuchen]

close it since it has been resolved.