Fix VQD's optimal_values (#10279) (#10312)

* Fix optimal values * Add unittest * Add reno * Update unittest * Revert "Update unittest" This reverts commit 5000d2f. * Update test * Make test subtest (cherry picked from commit 93a8172) Co-authored-by: Elena Peña Tapia <[email protected]>
Qiskit · Jun 20, 2023 · 485eb76 · 485eb76
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diff --git a/qiskit/algorithms/eigensolvers/vqd.py b/qiskit/algorithms/eigensolvers/vqd.py
@@ -448,7 +448,7 @@ def _update_vqd_result(
             else np.array([opt_result.x])
         )
         result.optimal_parameters.append(dict(zip(ansatz.parameters, opt_result.x)))
-        result.optimal_values = np.concatenate([result.optimal_points, [opt_result.x]])
+        result.optimal_values = np.concatenate([result.optimal_values, [opt_result.fun]])
         result.cost_function_evals = np.concatenate([result.cost_function_evals, [opt_result.nfev]])
         result.optimizer_times = np.concatenate([result.optimizer_times, [eval_time]])
         result.eigenvalues.append(opt_result.fun + 0j)

diff --git a/releasenotes/notes/fix-vqd-result-27b26f0a6d49e7c7.yaml b/releasenotes/notes/fix-vqd-result-27b26f0a6d49e7c7.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+     Fixed bug in :class:`~qiskit.algorithms.eigensolvers.VQD` where ``result.optimal_values`` was a
+     copy of ``result.optimal_points``. It now returns the corresponding values.
diff --git a/test/python/algorithms/eigensolvers/test_vqd.py b/test/python/algorithms/eigensolvers/test_vqd.py
@@ -103,6 +103,11 @@ def test_basic_operator(self, op):
             )
             np.testing.assert_array_almost_equal(job.result().values, result.eigenvalues, 6)
 
+        with self.subTest(msg="assert returned values are eigenvalues"):
+            np.testing.assert_array_almost_equal(
+                result.optimal_values, self.h2_energy_excited[:2], decimal=3
+            )
+
     def test_full_spectrum(self):
         """Test obtaining all eigenvalues."""
         vqd = VQD(self.estimator, self.fidelity, self.ryrz_wavefunction, optimizer=L_BFGS_B(), k=4)