Define state method and returns_state=True in capabilities (#101)

* matrix update * matrix update * def state * def state + capabilities * test dev.state * changelog * linting * write dev._state instead of dev.state
PennyLaneAI · Jun 8, 2022 · ddfd8e5 · ddfd8e5
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,4 +1,4 @@
-# Release 0.21.0-dev
+# Release 0.24.0-dev
 
 ### New features since last release
 
@@ -10,10 +10,17 @@
 
 ### Bug fixes
 
+* Defines the missing `state` method and `returns_state` entry of the
+  `capabilities` dictionary for `forest.wavefunction` and
+  `forest.numpy_wavefunction`.
+  [(#36)](https://github.com/PennyLaneAI/pennylane-qulacs/pull/36)
+
 ### Contributors
 
 This release contains contributions from (in alphabetical order):
 
+Antal Száva.
+
 ---
 
 # Release 0.20.0

diff --git a/pennylane_forest/numpy_wavefunction.py b/pennylane_forest/numpy_wavefunction.py
@@ -19,10 +19,6 @@
 Code details
 ~~~~~~~~~~~~
 """
-import itertools
-
-import numpy as np
-
 from pyquil.pyqvm import PyQVM
 from pyquil.simulation import NumpyWavefunctionSimulator
 
@@ -50,6 +46,18 @@ def __init__(self, wires, *, shots=None, **kwargs):
         self.qc = PyQVM(n_qubits=len(self.wires), quantum_simulator_type=NumpyWavefunctionSimulator)
         self._state = None
 
+    @classmethod
+    def capabilities(cls):  # pylint: disable=missing-function-docstring
+        capabilities = super().capabilities().copy()
+        capabilities.update(
+            returns_state=True,
+        )
+        return capabilities
+
+    @property
+    def state(self):  # pylint: disable=missing-function-docstring
+        return self._state
+
     def apply(self, operations, **kwargs):
         self.reset()
         self.qc.wf_simulator.reset()

diff --git a/pennylane_forest/wavefunction.py b/pennylane_forest/wavefunction.py
@@ -26,11 +26,7 @@
 Code details
 ~~~~~~~~~~~~
 """
-import itertools
-
 import numpy as np
-from numpy.linalg import eigh
-from pennylane.wires import Wires
 
 from pyquil.api import WavefunctionSimulator
 
@@ -105,6 +101,18 @@ def bit2dec(x):
             y += j << i
         return y
 
+    @classmethod
+    def capabilities(cls):  # pylint: disable=missing-function-docstring
+        capabilities = super().capabilities().copy()
+        capabilities.update(
+            returns_state=True,
+        )
+        return capabilities
+
+    @property
+    def state(self):  # pylint: disable=missing-function-docstring
+        return self._state
+
     def expand_state(self):
         """The pyQuil wavefunction simulator initializes qubits dymnically as they are requested.
         This method expands the state to the full number of wires in the device."""

diff --git a/tests/test_numpy_wavefunction.py b/tests/test_numpy_wavefunction.py
@@ -122,7 +122,7 @@ def test_apply(self, op, apply_unitary, tol):
         dev.apply(tape.operations, rotations=tape.diagonalizing_gates)
 
         # verify the device is now in the expected state
-        self.assertAllAlmostEqual(dev._state, state, delta=tol)
+        self.assertAllAlmostEqual(dev.state, state, delta=tol)
 
     def test_sample_values(self, tol):
         """Tests if the samples returned by sample have

diff --git a/tests/test_wavefunction.py b/tests/test_wavefunction.py
@@ -122,7 +122,7 @@ def test_apply(self, op, apply_unitary, tol):
         dev.apply(tape.operations, rotations=tape.diagonalizing_gates)
 
         # verify the device is now in the expected state
-        self.assertAllAlmostEqual(dev._state, state, delta=tol)
+        self.assertAllAlmostEqual(dev.state, state, delta=tol)
 
     def test_sample_values(self, tol):
         """Tests if the samples returned by sample have
@@ -390,13 +390,13 @@ def test_expand_state(self):
         dev._state = np.array([0, 1, 1, 0]) / np.sqrt(2)
         dev._active_wires = Wires([0, 2])
         dev.expand_state()
-        self.assertAllEqual(dev._state, np.array([0, 1, 0, 0, 1, 0, 0, 0]) / np.sqrt(2))
+        self.assertAllEqual(dev.state, np.array([0, 1, 0, 0, 1, 0, 0, 0]) / np.sqrt(2))
 
         # expand a three qubit state to the 3 qubit device
         dev._state = np.array([0, 1, 1, 0, 0, 1, 1, 0]) / 2
         dev._active_wires = Wires([0, 1, 2])
         dev.expand_state()
-        self.assertAllEqual(dev._state, np.array([0, 1, 1, 0, 0, 1, 1, 0]) / 2)
+        self.assertAllEqual(dev.state, np.array([0, 1, 1, 0, 0, 1, 1, 0]) / 2)
 
 
     @pytest.mark.parametrize("bitstring, dec", [([1], 1), ([0,0,1], 1), ([0,1,0], 2), ([1,1,1], 7)])