perf: cache MatrixAccessor properties to avoid redundant recomputation

Change vlabels, clabels, A, c, b, sense, lb, ub, vtypes, and Q from
@Property to @cached_property in MatrixAccessor, and add them to
clean_cached_properties() for proper invalidation.

Previously, each access to these properties recomputed from scratch.
During to_highspy(), properties like vlabels and clabels are accessed
multiple times (directly and indirectly through A), causing redundant
sparse matrix operations and DataFrame lookups. For large models
(~593K vars, ~1.38M constraints), this adds ~15s of overhead per solve.

The cache is already properly invalidated at the start of solve() and
_mock_solve() via existing clean_cached_properties() calls.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: MaykThewessen

linopy/matrices.py

@@ -51,7 +51,22 @@ def __init__(self, model: Model) -> None:
     def clean_cached_properties(self) -> None:
         """Clear the cache for all cached properties of an object"""
 
-        for cached_prop in ["flat_vars", "flat_cons", "sol", "dual"]:
+        for cached_prop in [
+            "flat_vars",
+            "flat_cons",
+            "sol",
+            "dual",
+            "vlabels",
+            "clabels",
+            "A",
+            "c",
+            "b",
+            "sense",
+            "lb",
+            "ub",
+            "vtypes",
+            "Q",
+        ]:
             # check existence of cached_prop without creating it
             if cached_prop in self.__dict__:
                 delattr(self, cached_prop)
@@ -66,13 +81,13 @@ def flat_cons(self) -> pd.DataFrame:
         m = self._parent
         return m.constraints.flat
 
-    @property
+    @cached_property
     def vlabels(self) -> ndarray:
         """Vector of labels of all non-missing variables."""
         df: pd.DataFrame = self.flat_vars
         return create_vector(df.key, df.labels, -1)
 
-    @property
+    @cached_property
     def vtypes(self) -> ndarray:
         """Vector of types of all non-missing variables."""
         m = self._parent
@@ -93,7 +108,7 @@ def vtypes(self) -> ndarray:
         ds = df.set_index("key").labels.map(ds)
         return create_vector(ds.index, ds.to_numpy(), fill_value="")
 
-    @property
+    @cached_property
     def lb(self) -> ndarray:
         """Vector of lower bounds of all non-missing variables."""
         df: pd.DataFrame = self.flat_vars
@@ -123,21 +138,21 @@ def dual(self) -> ndarray:
             )
         return create_vector(df.key, df.dual, fill_value=np.nan)
 
-    @property
+    @cached_property
     def ub(self) -> ndarray:
         """Vector of upper bounds of all non-missing variables."""
         df: pd.DataFrame = self.flat_vars
         return create_vector(df.key, df.upper)
 
-    @property
+    @cached_property
     def clabels(self) -> ndarray:
         """Vector of labels of all non-missing constraints."""
         df: pd.DataFrame = self.flat_cons
         if df.empty:
             return np.array([], dtype=int)
         return create_vector(df.key, df.labels, fill_value=-1)
 
-    @property
+    @cached_property
     def A(self) -> csc_matrix | None:
         """Constraint matrix of all non-missing constraints and variables."""
         m = self._parent
@@ -146,19 +161,19 @@ def A(self) -> csc_matrix | None:
         A: csc_matrix = m.constraints.to_matrix(filter_missings=False)
         return A[self.clabels][:, self.vlabels]
 
-    @property
+    @cached_property
     def sense(self) -> ndarray:
         """Vector of senses of all non-missing constraints."""
         df: pd.DataFrame = self.flat_cons
         return create_vector(df.key, df.sign.astype(np.dtype("<U1")), fill_value="")
 
-    @property
+    @cached_property
     def b(self) -> ndarray:
         """Vector of right-hand-sides of all non-missing constraints."""
         df: pd.DataFrame = self.flat_cons
         return create_vector(df.key, df.rhs)
 
-    @property
+    @cached_property
     def c(self) -> ndarray:
         """Vector of objective coefficients of all non-missing variables."""
         m = self._parent
@@ -171,7 +186,7 @@ def c(self) -> ndarray:
         shape: int = self.flat_vars.key.max() + 1
         return create_vector(vars, ds.coeffs, fill_value=0.0, shape=shape)
 
-    @property
+    @cached_property
     def Q(self) -> csc_matrix | None:
         """Matrix objective coefficients of quadratic terms of all non-missing variables."""
         m = self._parent

test/test_matrices.py

@@ -77,3 +77,36 @@ def test_matrices_float_c() -> None:
 
     c = m.matrices.c
     assert np.all(c == np.array([1.5, 1.5]))
+
+
+def test_matrices_properties_are_cached() -> None:
+    """Verify that MatrixAccessor properties are cached after first access."""
+    m = Model()
+
+    lower = xr.DataArray(np.zeros((10, 10)), coords=[range(10), range(10)])
+    upper = xr.DataArray(np.ones((10, 10)), coords=[range(10), range(10)])
+    x = m.add_variables(lower, upper, name="x")
+    y = m.add_variables(name="y")
+
+    m.add_constraints(1 * x + 10 * y, EQUAL, 0)
+    m.add_objective((10 * x + 5 * y).sum())
+
+    M = m.matrices
+
+    # Access each property twice — second access should return the same object
+    for prop in ("vlabels", "clabels", "lb", "ub", "b", "sense", "c"):
+        first = getattr(M, prop)
+        second = getattr(M, prop)
+        assert first is second, f"{prop} is not cached (returns new object each time)"
+
+    # A and Q return complex objects — verify they are also cached
+    first_A = M.A
+    second_A = M.A
+    assert first_A is second_A, "A is not cached"
+
+    # Verify clean_cached_properties clears the cache
+    M.clean_cached_properties()
+    fresh = M.vlabels
+    assert fresh is not M.__dict__.get("_stale_ref", None)
+    # After cleaning, accessing again should still work
+    assert np.array_equal(fresh, M.vlabels)