Add deprecation warning to algs module

qiskit/algorithms/__init__.py

@@ -14,6 +14,15 @@
 =====================================
 Algorithms (:mod:`qiskit.algorithms`)
 =====================================
+
+.. deprecated:: 0.25.0
+
+    The :mod:`qiskit.algorithms` module has been migrated to an independent package:
+    [LINK_PLACEHOLDER].
+    The current import path is deprecated and will be removed no earlier
+    than 3 months after the release date. You can run ``pip install qiskit_algorithms``
+    and import ``from qiskit_algorithms`` instead.
+
 It contains a collection of quantum algorithms, for use with quantum computers, to
 carry out research and investigate how to solve problems in different domains on
 near-term quantum devices with short depth circuits.
@@ -297,6 +306,8 @@
    AlgorithmJob
 
 """
+import warnings
+
 from .algorithm_job import AlgorithmJob
 from .algorithm_result import AlgorithmResult
 from .evolvers import EvolutionResult, EvolutionProblem
@@ -412,3 +423,13 @@
     "VarQTE",
     "VarQTEResult",
 ]
+
+warnings.warn(
+    "``qiskit.algorithms`` has been migrated to an independent package: "
+    "[LINK_PLACEHOLDER]."
+    "The ``qiskit.algorithms`` import path is deprecated as of qiskit-terra 0.25.0 and"
+    "will be removed no earlier than 3 months after the release date. "
+    "Please run ``pip install qiskit_algorithms`` and use ``import qiskit_algorithms`` instead.",
+    category=DeprecationWarning,
+    stacklevel=2,
+)