ENH make_sparse_spd_matrix use sparse memory layout (scikit-learn#2…

…7438)

doc/whats_new/v1.4.rst

@@ -113,7 +113,8 @@ and classes are impacted:
 - :class:`impute.KNNImputer` in :pr:`27277` by :user:`Yao Xiao <Charlie-XIAO>`;
 - :class:`kernel_approximation.PolynomialCountSketch` in  :pr:`27301` by
   :user:`Lohit SundaramahaLingam <lohitslohit>`;
-- :class:`neural_network.BernoulliRBM` in :pr:`27252` by `Yao Xiao <Charlie-XIAO>`.
+- :class:`neural_network.BernoulliRBM` in :pr:`27252` by
+  :user:`Yao Xiao <Charlie-XIAO>`.
 
 Changelog
 ---------
@@ -168,6 +169,15 @@ Changelog
   `kdtree` and `balltree` values will be removed in 1.6.
   :pr:`26744` by :user:`Shreesha Kumar Bhat <Shreesha3112>`.
 
+:mod:`sklearn.datasets`
+.......................
+
+- |Enhancement| :func:`datasets.make_sparse_spd_matrix` now uses a more memory-
+  efficient sparse layout. It also accepts a new keyword `sparse_format` that allows
+  specifying the output format of the sparse matrix. By default `sparse_format=None`,
+  which returns a dense numpy ndarray as before.
+  :pr:`27438` by :user:`Yao Xiao <Charlie-XIAO>`.
+
 :mod:`sklearn.decomposition`
 ............................
 

sklearn/datasets/_samples_generator.py

@@ -1573,6 +1573,10 @@ def make_spd_matrix(n_dim, *, random_state=None):
         "norm_diag": ["boolean"],
         "smallest_coef": [Interval(Real, 0, 1, closed="both")],
         "largest_coef": [Interval(Real, 0, 1, closed="both")],
+        "sparse_format": [
+            StrOptions({"bsr", "coo", "csc", "csr", "dia", "dok", "lil"}),
+            None,
+        ],
         "random_state": ["random_state"],
     },
     prefer_skip_nested_validation=True,
@@ -1584,6 +1588,7 @@ def make_sparse_spd_matrix(
     norm_diag=False,
     smallest_coef=0.1,
     largest_coef=0.9,
+    sparse_format=None,
     random_state=None,
 ):
     """Generate a sparse symmetric definite positive matrix.
@@ -1609,6 +1614,12 @@ def make_sparse_spd_matrix(
     largest_coef : float, default=0.9
         The value of the largest coefficient between 0 and 1.
 
+    sparse_format : str, default=None
+        String representing the output sparse format, such as 'csc', 'csr', etc.
+        If ``None``, return a dense numpy ndarray.
+
+        .. versionadded:: 1.4
+
     random_state : int, RandomState instance or None, default=None
         Determines random number generation for dataset creation. Pass an int
         for reproducible output across multiple function calls.
@@ -1631,30 +1642,35 @@ def make_sparse_spd_matrix(
     """
     random_state = check_random_state(random_state)
 
-    chol = -np.eye(dim)
-    aux = random_state.uniform(size=(dim, dim))
-    aux[aux < alpha] = 0
-    aux[aux > alpha] = smallest_coef + (
-        largest_coef - smallest_coef
-    ) * random_state.uniform(size=np.sum(aux > alpha))
-    aux = np.tril(aux, k=-1)
+    chol = -sp.eye(dim)
+    aux = sp.random(
+        m=dim,
+        n=dim,
+        density=1 - alpha,
+        data_rvs=lambda x: random_state.uniform(
+            low=smallest_coef, high=largest_coef, size=x
+        ),
+        random_state=random_state,
+    )
+    # We need to avoid "coo" format because it does not support slicing
+    aux = sp.tril(aux, k=-1, format="csc")
 
     # Permute the lines: we don't want to have asymmetries in the final
     # SPD matrix
     permutation = random_state.permutation(dim)
     aux = aux[permutation].T[permutation]
     chol += aux
-    prec = np.dot(chol.T, chol)
+    prec = chol.T @ chol
 
     if norm_diag:
         # Form the diagonal vector into a row matrix
-        d = np.diag(prec).reshape(1, prec.shape[0])
-        d = 1.0 / np.sqrt(d)
+        d = sp.diags(1.0 / np.sqrt(prec.diagonal()))
+        prec = d @ prec @ d
 
-        prec *= d
-        prec *= d.T
-
-    return prec
+    if sparse_format is None:
+        return prec.toarray()
+    else:
+        return prec.asformat(sparse_format)
 
 
 @validate_params(

sklearn/datasets/tests/test_samples_generator.py

@@ -22,12 +22,14 @@
     make_regression,
     make_s_curve,
     make_sparse_coded_signal,
+    make_sparse_spd_matrix,
     make_sparse_uncorrelated,
     make_spd_matrix,
     make_swiss_roll,
 )
 from sklearn.utils._testing import (
     assert_allclose,
+    assert_allclose_dense_sparse,
     assert_almost_equal,
     assert_array_almost_equal,
     assert_array_equal,
@@ -549,10 +551,42 @@ def test_make_spd_matrix():
     from numpy.linalg import eig
 
     eigenvalues, _ = eig(X)
-    assert_array_equal(
-        eigenvalues > 0, np.array([True] * 5), "X is not positive-definite"
+    assert np.all(eigenvalues > 0), "X is not positive-definite"
+
+
+@pytest.mark.parametrize("norm_diag", [True, False])
+@pytest.mark.parametrize(
+    "sparse_format", [None, "bsr", "coo", "csc", "csr", "dia", "dok", "lil"]
+)
+def test_make_sparse_spd_matrix(norm_diag, sparse_format, global_random_seed):
+    dim = 5
+    X = make_sparse_spd_matrix(
+        dim=dim,
+        norm_diag=norm_diag,
+        sparse_format=sparse_format,
+        random_state=global_random_seed,
     )
 
+    assert X.shape == (dim, dim), "X shape mismatch"
+    if sparse_format is None:
+        assert not sp.issparse(X)
+        assert_allclose(X, X.T)
+        Xarr = X
+    else:
+        assert sp.issparse(X) and X.format == sparse_format
+        assert_allclose_dense_sparse(X, X.T)
+        Xarr = X.toarray()
+
+    from numpy.linalg import eig
+
+    # Do not use scipy.sparse.linalg.eigs because it cannot find all eigenvalues
+    eigenvalues, _ = eig(Xarr)
+    assert np.all(eigenvalues > 0), "X is not positive-definite"
+
+    if norm_diag:
+        # Check that leading diagonal elements are 1
+        assert_array_almost_equal(Xarr.diagonal(), np.ones(dim))
+
 
 @pytest.mark.parametrize("hole", [False, True])
 def test_make_swiss_roll(hole):