[Stable] Backport to stable (#1048, #1049, #1052, #1055) (#1056)

* CircuitOp uses QuantumCircuit.compose, not .combine (Qiskit#1048)

* MatrixOp.to_instruction updated to return an Instruction (Qiskit#1049)

* Fix hash function of PauliOp class (#1052)

* Fix hash function of PauliOp class

This change replaces the use of the `id()` function in the `PauliOp`
hash function with the hash of its string representation. This is inline
with the hash function of the `Pauli` class.

This fix is necessary, since prior to this change, a set comparison
including instances of identical `PauliOp`s would fail, because sets
rely on hash tables.

A regression test to ensure the working state after this commit is
included, too.

Credits for spotting and collaborating in fixing the bug go to @Cryoris

* Add releasenote

Co-authored-by: Julien Gacon <jules.gacon@googlemail.com>

* Make cvxpy an optional dependency (Qiskit#1055)

Co-authored-by: Julien Gacon <jules.gacon@googlemail.com>
Co-authored-by: Max Rossmannek <oss@zurich.ibm.com>
Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

.pylintdict

@@ -116,6 +116,7 @@ ctls
 cts
 currentmodule
 cvs
+cvxpy
 cx
 cx's
 cz

.travis.yml

@@ -130,6 +130,7 @@ jobs:
         - sudo apt-get -y install hunspell-en-us
         - pip install pyenchant
         - pip install cplex
+        - pip install "cvxpy>1.0.0,<1.1.0"
       script:
         - make spell
         - make style
@@ -148,6 +149,7 @@ jobs:
             - aqua137.dep
       before_script:
         - pip install cplex
+        - pip install "cvxpy>1.0.0,<1.1.0"
         - export PYTHON="coverage3 run --source qiskit/aqua,qiskit/chemistry,qiskit/finance,qiskit/ml,qiskit/optimization --omit */gauopen/* --parallel-mode"
       script:
         - stestr --test-path test/aqua run --blacklist-file selection.txt 2> >(tee /dev/stderr out.txt > /dev/null)
@@ -162,6 +164,8 @@ jobs:
           name: aqua138
           paths: aqua138.dep
       python: 3.8
+      before_script:
+        - pip install "cvxpy>1.0.0,<1.1.0"
       script:
         - stestr --test-path test/aqua run --blacklist-file selection.txt 2> >(tee /dev/stderr out.txt > /dev/null)
         - python tools/extract_deprecation.py -file out.txt -output aqua138.dep
@@ -176,6 +180,7 @@ jobs:
             - aqua237.dep
       before_script:
         - pip install cplex
+        - pip install "cvxpy>1.0.0,<1.1.0"
         - export PYTHON="coverage3 run --source qiskit/aqua,qiskit/chemistry,qiskit/finance,qiskit/ml,qiskit/optimization --omit */gauopen/* --parallel-mode"
       script:
         - stestr --test-path test/aqua run --whitelist-file selection.txt 2> >(tee /dev/stderr out.txt > /dev/null)
@@ -190,6 +195,8 @@ jobs:
           name: aqua238
           paths: aqua238.dep
       python: 3.8
+      before_script:
+        - pip install "cvxpy>1.0.0,<1.1.0"
       script:
         - stestr --test-path test/aqua run --whitelist-file selection.txt 2> >(tee /dev/stderr out.txt > /dev/null)
         - python tools/extract_deprecation.py -file out.txt -output aqua238.dep
@@ -328,7 +335,7 @@ jobs:
       if: tag IS blank
       script:
         - pip install cplex
-        - pip install cvxopt
+        - pip install "cvxpy>1.0.0,<1.1.0"
         - pip install https://github.com/rpmuller/pyquante2/archive/master.zip --progress-bar off
         - pip check
     - stage: Deprecation Messages

qiskit/aqua/operators/primitive_ops/circuit_op.py

@@ -125,7 +125,7 @@ def compose(self, other: OperatorBase) -> OperatorBase:
             other = other.to_circuit_op()
 
         if isinstance(other, (CircuitOp, CircuitStateFn)):
-            new_qc = other.primitive.combine(self.primitive)
+            new_qc = other.primitive.compose(self.primitive)  # type: ignore
             if isinstance(other, CircuitStateFn):
                 return CircuitStateFn(new_qc,
                                       is_measurement=other.is_measurement,

qiskit/aqua/operators/primitive_ops/matrix_op.py

@@ -162,7 +162,7 @@ def to_matrix_op(self, massive: bool = False) -> OperatorBase:
         return self
 
     def to_instruction(self) -> Instruction:
-        return PrimitiveOp(self.primitive.to_instruction(), coeff=self.coeff)
+        return (self.coeff * self.primitive).to_instruction()  # type: ignore
 
     def to_legacy_op(self, massive: bool = False) -> MatrixOperator:
         return MatrixOperator(self.to_matrix(massive=massive))

qiskit/aqua/operators/primitive_ops/pauli_op.py

@@ -233,7 +233,7 @@ def exp_i(self) -> OperatorBase:
 
     def __hash__(self) -> int:
         # Need this to be able to easily construct AbelianGraphs
-        return id(self)
+        return hash(str(self))
 
     def commutes(self, other_op: OperatorBase) -> bool:
         """ Returns whether self commutes with other_op.

qiskit/aqua/utils/qp_solver.py

@@ -18,7 +18,11 @@
 import logging
 
 import numpy as np
-import cvxpy
+try:
+    import cvxpy
+    HAS_CVX = True
+except ImportError:
+    HAS_CVX = False
 
 logger = logging.getLogger(__name__)
 
@@ -43,8 +47,15 @@ def optimize_svm(kernel_matrix: np.ndarray,
         np.ndarray: Sx1 array, where S is the number of supports
         np.ndarray: Sx1 array, where S is the number of supports
         np.ndarray: Sx1 array, where S is the number of supports
+
+    Raises:
+        NameError: If cvxpy is not installed
     """
     # pylint: disable=invalid-name, unused-argument
+    if not HAS_CVX:
+        raise NameError("The CVXPY package is required to use the "
+                        "optimize_svm() function. You can install it with "
+                        "'pip install qiskit-aqua[cvx]'.")
     if y.ndim == 1:
         y = y[:, np.newaxis]
     H = np.outer(y, y) * kernel_matrix

releasenotes/notes/circuit-op-compose-register-indep-5f3fd76dbb75c84e.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    The ``compose`` method of the ``CircuitOp`` used ``QuantumCircuit.combine`` which has been
+    changed to use ``QuantumCircuit.compose``. Using combine leads to the problem that composing
+    an operator with a ``CircuitOp`` based on a named register does not chain the operators but
+    stacks them. E.g. composing ``Z ^ 2`` with a circuit based on a 2-qubit named register yielded
+    a 4-qubit operator instead of a 2-qubit operator.

releasenotes/notes/cvx-optional-e44920f87cff5e8d.yaml

@@ -0,0 +1,10 @@
+---
+upgrade:
+  - |
+    The ``cvxpy <https://www.cvxpy.org/>`_ dependency which is required for
+    the the svm classifier has been removed from the requirements list and made
+    an optional dependency. This is because installing cvxpy is not seamless
+    in every environment and often requires a compiler be installed to run.
+    To use the svm classifier now you'll need to install cvxpy by either
+    running ``pip install cvxpy<1.1.0`` or to install it with aqua running
+    ``pip install qiskit-aqua[cvx]``.

releasenotes/notes/matrix-op-to-instruction-a990ec3a3db8ca8d.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    The ``MatrixOp.to_instruction`` method previously returned an operator and not
+    an instruction. This method has been updated to return an Instruction.
+    Note that this only works if the operator primitive is unitary, otherwise
+    an error is raised upon the construction of the instruction.

releasenotes/notes/pauli-op-hash-fix-c8f8bbc6fbccd04e.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    The ``__hash__`` method of the ``PauliOp`` class used the ``id()`` method
+    which prevents set comparisons to work as expected since they rely on hash
+    tables and identical objects used to not have identical hashes. Now, the
+    implementation uses a hash of the string representation inline with the
+    implementation in the ``Pauli`` class.

setup.py

@@ -41,7 +41,6 @@
     "h5py",
     "networkx>=2.2",
     "pyscf; sys_platform != 'win32'",
-    'cvxpy>1.0.0,<1.1.0',
 ]
 
 if not hasattr(setuptools, 'find_namespace_packages') or not inspect.ismethod(setuptools.find_namespace_packages):
@@ -86,6 +85,7 @@
     extras_require={
         'torch': ["torch; sys_platform == 'linux' or (python_version < '3.8' and sys_platform != 'win32')"],
         'cplex': ["cplex; python_version >= '3.6' and python_version < '3.8'"],
+        'cvx': ['cvxpy>1.0.0,<1.1.0'],
     },
     zip_safe=False
 )

test/aqua/operators/test_op_construction.py

@@ -19,11 +19,14 @@
 import itertools
 import numpy as np
 
-from qiskit import QuantumCircuit
+from qiskit.circuit import QuantumCircuit, QuantumRegister, Instruction
+from qiskit.extensions.exceptions import ExtensionError
 from qiskit.quantum_info.operators import Operator, Pauli
 from qiskit.circuit.library import CZGate
 
-from qiskit.aqua.operators import X, Y, Z, I, CX, T, H, PrimitiveOp, SummedOp, PauliOp, Minus
+from qiskit.aqua.operators import (
+    X, Y, Z, I, CX, T, H, PrimitiveOp, SummedOp, PauliOp, Minus, CircuitOp
+)
 
 
 # pylint: disable=invalid-name
@@ -182,6 +185,17 @@ def test_to_matrix(self):
         np.testing.assert_array_almost_equal(
             op6.to_matrix(), op5.to_matrix() + Operator.from_label('+r').data)
 
+    def test_matrix_to_instruction(self):
+        """Test MatrixOp.to_instruction yields an Instruction object."""
+        matop = (H ^ 3).to_matrix_op()
+        with self.subTest('assert to_instruction returns Instruction'):
+            self.assertIsInstance(matop.to_instruction(), Instruction)
+
+        matop = ((H ^ 3) + (Z ^ 3)).to_matrix_op()
+        with self.subTest('matrix operator is not unitary'):
+            with self.assertRaises(ExtensionError):
+                matop.to_instruction()
+
     def test_adjoint(self):
         """ adjoint test """
         gnarly_op = 3 * (H ^ I ^ Y).compose(X ^ X ^ Z).tensor(T ^ Z) + \
@@ -221,6 +235,26 @@ def test_circuit_permute(self):
         c_op_id = c_op_perm.permute(perm)
         self.assertEqual(c_op, c_op_id)
 
+    def test_circuit_compose_register_independent(self):
+        """Test that CircuitOp uses combines circuits independent of the register.
+
+        I.e. that is uses ``QuantumCircuit.compose`` over ``combine`` or ``extend``.
+        """
+        op = Z ^ 2
+        qr = QuantumRegister(2, 'my_qr')
+        circuit = QuantumCircuit(qr)
+        composed = op.compose(CircuitOp(circuit))
+
+        self.assertEqual(composed.num_qubits, 2)
+
+    def test_pauli_op_hashing(self):
+        """Regression test against faulty set comparison.
+
+        Set comparisons rely on a hash table which requires identical objects to have identical
+        hashes. Thus, the PauliOp.__hash__ should support this requirement.
+        """
+        self.assertEqual(set([2*Z]), set([2*Z]))
+
 
 if __name__ == '__main__':
     unittest.main()