LinOp arithmetic part 1

src/probnum/_config.py

@@ -130,10 +130,19 @@ def register(self, key: str, default_value: Any, description: str) -> None:
         "matrix_free",
         False,
         (
-            "If True, wherever possible, LinearOperators are used instead "
-            "of arrays. LinearOperators define a matrix-vector product implicitly without instantiating the full matrix in memory. This makes them memory- and runtime-efficient for linear algebra operations."
+            "If ``True``, wherever possible, ``LinearOperator`` s are used instead "
+            "of arrays. ``LinearOperator`` s define a matrix-vector product implicitly without "
+            "instantiating the full matrix in memory. This makes them memory- and runtime-efficient "
+            "for linear algebra operations."
         ),
     ),
+    (
+        "lazy_matrix_matrix_matmul",
+        False,
+        "If ``True``, the matmul operation applied to two ``Matrix``-``LinearOperator`` s will "
+        "again yield a ``Matrix``-``LinearOperator`` with the computed matrix-matrix product,"
+        " instead of a ``ProductLinearOperator``.",
+    ),
 ]
 
 # ... and register the default configuration options.

src/probnum/linops/__init__.py

@@ -12,30 +12,38 @@
 :class:`~probnum.linops.LinearOperator` instances.
 """
 
-from ._kronecker import Kronecker, SymmetricKronecker, Symmetrize
-from ._linear_operator import Identity, LinearOperator, Matrix
-from ._scaling import Scaling
+from ._kronecker import IdentityKronecker, Kronecker, SymmetricKronecker, Symmetrize
+from ._linear_operator import Embedding, Identity, LinearOperator, Matrix, Selection
+from ._scaling import Scaling, Zero
 from ._utils import LinearOperatorLike, aslinop
 
 # Public classes and functions. Order is reflected in documentation.
 __all__ = [
     "aslinop",
+    "Embedding",
     "LinearOperator",
     "Matrix",
     "Identity",
+    "IdentityKronecker",
     "Scaling",
     "Kronecker",
+    "Selection",
     "SymmetricKronecker",
     "Symmetrize",
+    "Zero",
 ]
 
 # Set correct module paths. Corrects links and module paths in documentation.
 LinearOperator.__module__ = "probnum.linops"
+Embedding.__module__ = "probnum.linops"
 Matrix.__module__ = "probnum.linops"
 Identity.__module__ = "probnum.linops"
+IdentityKronecker.__module__ = "probnum.linops"
 Scaling.__module__ = "probnum.linops"
 Kronecker.__module__ = "probnum.linops"
+Selection.__module__ = "probnum.linops"
 SymmetricKronecker.__module__ = "probnum.linops"
 Symmetrize.__module__ = "probnum.linops"
+Zero.__module__ = "probnum.linops"
 
 aslinop.__module__ = "probnum.linops"