From 359cbaf517055fa9de89d7bdd743c1c5718b439d Mon Sep 17 00:00:00 2001
From: Edoardo Altamura <38359901+edoaltamura@users.noreply.github.com>
Date: Thu, 15 May 2025 14:47:12 +0100
Subject: [PATCH 1/4] Port optimizer update from Algorithms

---
 .pylintdict                                   |  6 ++-
 .../optimizers/__init__.py                    | 13 ++++++-
 .../optimizers/nlopts/nloptimizer.py          |  6 ++-
 .../optimizers/nlopts/sbplx.py                | 37 +++++++++++++++++++
 .../add-sbplx-optimizer-d23fb5925879fdae.yaml |  8 ++++
 test/optimizers/test_optimizers.py            |  4 +-
 6 files changed, 69 insertions(+), 5 deletions(-)
 create mode 100644 qiskit_machine_learning/optimizers/nlopts/sbplx.py
 create mode 100644 releasenotes/notes/add-sbplx-optimizer-d23fb5925879fdae.yaml

diff --git a/.pylintdict b/.pylintdict
index 34bef92c3..5942e917c 100644
--- a/.pylintdict
+++ b/.pylintdict
@@ -253,6 +253,7 @@ izaac
 izz
 jac
 jacobian
+johnson
 jm
 jonathan
 jones
@@ -487,6 +488,7 @@ sanjiv
 sashank
 satisfiability
 satyen
+sbplx
 scalability
 schroediger
 schroedinger
@@ -529,6 +531,7 @@ stdout
 stefano
 steppable
 stepsize
+steven
 str
 stratifications
 stratification
@@ -536,6 +539,7 @@ subcircuits
 subclassed
 subclasses
 subcomponents
+subplex
 submodules
 subobjects
 subseteq
@@ -627,4 +631,4 @@ zz
 ω
 φ_i
 φ_ij
-Δ
\ No newline at end of file
+Δ
diff --git a/qiskit_machine_learning/optimizers/__init__.py b/qiskit_machine_learning/optimizers/__init__.py
index 65102d931..5e989a622 100644
--- a/qiskit_machine_learning/optimizers/__init__.py
+++ b/qiskit_machine_learning/optimizers/__init__.py
@@ -1,6 +1,6 @@
 # This code is part of a Qiskit project.
 #
-# (C) Copyright IBM 2018, 2024.
+# (C) Copyright IBM 2018, 2025.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -91,6 +91,15 @@
 https://github.com/qiskit-community/qiskit-algorithms/issues/84.
 
 
+Qiskit also provides local optimizers based on
+`NLOpt <https://nlopt.readthedocs.io/en/latest/>`_.
+See Global Optimizers section below for the optional NLOpt installation instructions.
+.. autosummary::
+   :toctree: ../stubs/
+   :nosignatures:
+   SBPLX
+
+
 Global optimizers
 -----------------
 The global optimizers here all use `NLOpt <https://nlopt.readthedocs.io/en/latest/>`_ for their
@@ -123,6 +132,7 @@
 from .nlopts.direct_l_rand import DIRECT_L_RAND
 from .nlopts.esch import ESCH
 from .nlopts.isres import ISRES
+from .nlopts.sbplx import SBPLX
 from .steppable_optimizer import SteppableOptimizer, AskData, TellData, OptimizerState
 from .optimizer import Minimizer, Optimizer, OptimizerResult, OptimizerSupportLevel
 from .p_bfgs import P_BFGS
@@ -165,5 +175,6 @@
     "DIRECT_L_RAND",
     "ESCH",
     "ISRES",
+    "SBPLX",
     "UMDA",
 ]
diff --git a/qiskit_machine_learning/optimizers/nlopts/nloptimizer.py b/qiskit_machine_learning/optimizers/nlopts/nloptimizer.py
index d04e1d4d1..3c977fe89 100644
--- a/qiskit_machine_learning/optimizers/nlopts/nloptimizer.py
+++ b/qiskit_machine_learning/optimizers/nlopts/nloptimizer.py
@@ -1,6 +1,6 @@
 # This code is part of a Qiskit project.
 #
-# (C) Copyright IBM 2018, 2024.
+# (C) Copyright IBM 2018, 2025.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -33,12 +33,13 @@ class NLoptOptimizerType(Enum):
     GN_DIRECT_L = 3
     GN_ESCH = 4
     GN_ISRES = 5
+    LN_SBPLX = 6
 
 
 @_optionals.HAS_NLOPT.require_in_instance
 class NLoptOptimizer(Optimizer):
     """
-    NLopt global optimizer base class
+    NLopt local and global optimizer base class
     """
 
     _OPTIONS = ["max_evals"]
@@ -64,6 +65,7 @@ def __init__(self, max_evals: int = 1000) -> None:  # pylint: disable=unused-arg
             NLoptOptimizerType.GN_DIRECT_L: nlopt.GN_DIRECT_L,
             NLoptOptimizerType.GN_ESCH: nlopt.GN_ESCH,
             NLoptOptimizerType.GN_ISRES: nlopt.GN_ISRES,
+            NLoptOptimizerType.LN_SBPLX: nlopt.LN_SBPLX,
         }
 
     @abstractmethod
diff --git a/qiskit_machine_learning/optimizers/nlopts/sbplx.py b/qiskit_machine_learning/optimizers/nlopts/sbplx.py
new file mode 100644
index 000000000..96b88e101
--- /dev/null
+++ b/qiskit_machine_learning/optimizers/nlopts/sbplx.py
@@ -0,0 +1,37 @@
+# This code is part of a Qiskit project.
+#
+# (C) Copyright IBM 2025.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""Sbplx (Subplex) optimizer."""
+
+from .nloptimizer import NLoptOptimizer, NLoptOptimizerType
+
+
+class SBPLX(NLoptOptimizer):
+    """
+    Subplex optimizer.
+
+    "Subplex (a variant of Nelder-Mead that uses Nelder-Mead on a sequence of subspaces)
+    is claimed to be much more efficient and robust than the original Nelder-Mead,
+    while retaining the latter's facility with discontinuous objectives,
+    and in my experience these claims seem to be true in many cases.
+    (However, I'm not aware of any proof that Subplex is globally convergent,
+    and perhaps it may fail for some objectives like Nelder-Mead; YMMV.)"
+    Description by Steven G. Johnson, author of NLopt library.
+
+    NLopt local optimizer, derivative-free.
+    For further detail, please refer to
+    https://nlopt.readthedocs.io/en/latest/NLopt_Algorithms/#sbplx-based-on-subplex
+    """
+
+    def get_nlopt_optimizer(self) -> NLoptOptimizerType:
+        """Return NLopt optimizer type."""
+        return NLoptOptimizerType.LN_SBPLX
diff --git a/releasenotes/notes/add-sbplx-optimizer-d23fb5925879fdae.yaml b/releasenotes/notes/add-sbplx-optimizer-d23fb5925879fdae.yaml
new file mode 100644
index 000000000..4790ec6f6
--- /dev/null
+++ b/releasenotes/notes/add-sbplx-optimizer-d23fb5925879fdae.yaml
@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Support for :class:`.SBPLX` optimizer from NLopt library has been added.
+    SBPLX is a local gradient-free optimizer based on Nelder-Mead and
+    is expected to show better convergence behavior.
+    Further information about this optimizer and the others can be found in
+    the API ref for the :mod:`~qiskit_machine_learning.optimizers`.
diff --git a/test/optimizers/test_optimizers.py b/test/optimizers/test_optimizers.py
index 0ad5975f4..719dc76a1 100644
--- a/test/optimizers/test_optimizers.py
+++ b/test/optimizers/test_optimizers.py
@@ -1,6 +1,6 @@
 # This code is part of a Qiskit project.
 #
-# (C) Copyright IBM 2018, 2024.
+# (C) Copyright IBM 2018, 2025.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -39,6 +39,7 @@
     Optimizer,
     P_BFGS,
     POWELL,
+    SBPLX,
     SLSQP,
     SPSA,
     QNSPSA,
@@ -221,6 +222,7 @@ def test_scipy_optimizer_parse_bounds(self):
         (CRS, False),
         (DIRECT_L, False),
         (DIRECT_L_RAND, False),
+        (SBPLX, True),
     )
     @unpack
     def test_nlopt(self, optimizer_cls, use_bound):

From 19eab88176070c8ac68fa5073446924ee63294a0 Mon Sep 17 00:00:00 2001
From: Edoardo Altamura <38359901+edoaltamura@users.noreply.github.com>
Date: Thu, 15 May 2025 15:28:07 +0100
Subject: [PATCH 2/4] Fix indentation html

---
 qiskit_machine_learning/optimizers/__init__.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/qiskit_machine_learning/optimizers/__init__.py b/qiskit_machine_learning/optimizers/__init__.py
index 5e989a622..6e540c59b 100644
--- a/qiskit_machine_learning/optimizers/__init__.py
+++ b/qiskit_machine_learning/optimizers/__init__.py
@@ -83,6 +83,7 @@
    SciPyOptimizer
    UMDA
 
+
 The optimizers from
 `scikit-quant <https://scikit-quant.readthedocs.io/en/latest/>`_ are not included in the
 Qiskit Machine Learning library.

From 26f6bba8bf9cac4bda4ccd86bb49a2d3c1c569e8 Mon Sep 17 00:00:00 2001
From: Edoardo Altamura <38359901+edoaltamura@users.noreply.github.com>
Date: Thu, 15 May 2025 17:25:02 +0100
Subject: [PATCH 3/4] Fix indentation and polish up inits

---
 .../optimizers/__init__.py                    | 92 ++++++++++---------
 .../optimizers/nlopts/__init__.py             |  3 +-
 .../optimizers/nlopts/sbplx.py                | 11 +--
 3 files changed, 54 insertions(+), 52 deletions(-)

diff --git a/qiskit_machine_learning/optimizers/__init__.py b/qiskit_machine_learning/optimizers/__init__.py
index 6e540c59b..df5653478 100644
--- a/qiskit_machine_learning/optimizers/__init__.py
+++ b/qiskit_machine_learning/optimizers/__init__.py
@@ -32,56 +32,56 @@
 ----------------------
 
 .. autosummary::
-   :toctree: ../stubs/
-   :nosignatures:
+    :toctree: ../stubs/
+    :nosignatures:
 
-   OptimizerResult
-   Optimizer
-   Minimizer
+    OptimizerResult
+    Optimizer
+    Minimizer
 
 Steppable optimization
 ----------------------
 
 .. autosummary::
-   :toctree: ../stubs/
+    :toctree: ../stubs/
 
-   optimizer_utils
+    optimizer_utils
 
 .. autosummary::
-   :toctree: ../stubs/
-   :nosignatures:
+    :toctree: ../stubs/
+    :nosignatures:
 
-   SteppableOptimizer
-   AskData
-   TellData
-   OptimizerState
+    SteppableOptimizer
+    AskData
+    TellData
+    OptimizerState
 
 
 Local optimizers
 ----------------
 
 .. autosummary::
-   :toctree: ../stubs/
-   :nosignatures:
-
-   ADAM
-   AQGD
-   CG
-   COBYLA
-   L_BFGS_B
-   GSLS
-   GradientDescent
-   GradientDescentState
-   NELDER_MEAD
-   NFT
-   P_BFGS
-   POWELL
-   SLSQP
-   SPSA
-   QNSPSA
-   TNC
-   SciPyOptimizer
-   UMDA
+    :toctree: ../stubs/
+    :nosignatures:
+
+    ADAM
+    AQGD
+    CG
+    COBYLA
+    L_BFGS_B
+    GSLS
+    GradientDescent
+    GradientDescentState
+    NELDER_MEAD
+    NFT
+    P_BFGS
+    POWELL
+    SLSQP
+    SPSA
+    QNSPSA
+    TNC
+    SciPyOptimizer
+    UMDA
 
 
 The optimizers from
@@ -95,10 +95,12 @@
 Qiskit also provides local optimizers based on
 `NLOpt <https://nlopt.readthedocs.io/en/latest/>`_.
 See Global Optimizers section below for the optional NLOpt installation instructions.
+
 .. autosummary::
-   :toctree: ../stubs/
-   :nosignatures:
-   SBPLX
+    :toctree: ../stubs/
+    :nosignatures:
+
+    SBPLX
 
 
 Global optimizers
@@ -108,14 +110,14 @@
 To install the ``NLOpt`` dependent package you can use ``pip install nlopt``.
 
 .. autosummary::
-   :toctree: ../stubs/
-   :nosignatures:
-
-   CRS
-   DIRECT_L
-   DIRECT_L_RAND
-   ESCH
-   ISRES
+    :toctree: ../stubs/
+    :nosignatures:
+
+    CRS
+    DIRECT_L
+    DIRECT_L_RAND
+    ESCH
+    ISRES
 
 """
 
diff --git a/qiskit_machine_learning/optimizers/nlopts/__init__.py b/qiskit_machine_learning/optimizers/nlopts/__init__.py
index 59bf5f86c..b7e287391 100644
--- a/qiskit_machine_learning/optimizers/nlopts/__init__.py
+++ b/qiskit_machine_learning/optimizers/nlopts/__init__.py
@@ -10,11 +10,12 @@
 # copyright notice, and modified files need to carry a notice indicating
 # that they have been altered from the originals.
 
-"""NLopt based global optimizers"""
+"""NLopt-based global and local optimizers"""
 
 from .crs import CRS
 from .direct_l import DIRECT_L
 from .direct_l_rand import DIRECT_L_RAND
 from .esch import ESCH
 from .isres import ISRES
+from .sbplx import SBPLX
 from .nloptimizer import NLoptOptimizer
diff --git a/qiskit_machine_learning/optimizers/nlopts/sbplx.py b/qiskit_machine_learning/optimizers/nlopts/sbplx.py
index 96b88e101..d67991292 100644
--- a/qiskit_machine_learning/optimizers/nlopts/sbplx.py
+++ b/qiskit_machine_learning/optimizers/nlopts/sbplx.py
@@ -19,13 +19,12 @@ class SBPLX(NLoptOptimizer):
     """
     Subplex optimizer.
 
-    "Subplex (a variant of Nelder-Mead that uses Nelder-Mead on a sequence of subspaces)
+    'Subplex (a variant of Nelder-Mead that uses Nelder-Mead on a sequence of subspaces)
     is claimed to be much more efficient and robust than the original Nelder-Mead,
-    while retaining the latter's facility with discontinuous objectives,
-    and in my experience these claims seem to be true in many cases.
-    (However, I'm not aware of any proof that Subplex is globally convergent,
-    and perhaps it may fail for some objectives like Nelder-Mead; YMMV.)"
-    Description by Steven G. Johnson, author of NLopt library.
+    while retaining the latter's facility with discontinuous objectives.
+    While these claims seem to be true in many cases, we could not find any proof that
+    Subplex is globally convergent, and perhaps it may fail for some objective functions
+    like Nelder-Mead; YMMV.)', by Steven G. Johnson, author of NLopt library.
 
     NLopt local optimizer, derivative-free.
     For further detail, please refer to

From 17a57355a8e267654fefc29379a1d55083ad6469 Mon Sep 17 00:00:00 2001
From: Edoardo Altamura <38359901+edoaltamura@users.noreply.github.com>
Date: Fri, 16 May 2025 11:51:09 +0100
Subject: [PATCH 4/4] Fix copyright

---
 qiskit_machine_learning/optimizers/nlopts/__init__.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/qiskit_machine_learning/optimizers/nlopts/__init__.py b/qiskit_machine_learning/optimizers/nlopts/__init__.py
index b7e287391..4a2be93dd 100644
--- a/qiskit_machine_learning/optimizers/nlopts/__init__.py
+++ b/qiskit_machine_learning/optimizers/nlopts/__init__.py
@@ -1,6 +1,6 @@
 # This code is part of a Qiskit project.
 #
-# (C) Copyright IBM 2018, 2024.
+# (C) Copyright IBM 2018, 2025.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory