scikit-learn · Micky774 · Apr 2, 2023 · Mar 6, 2023 · Mar 17, 2023 · Mar 20, 2023
diff --git a/doc/whats_new/v1.3.rst b/doc/whats_new/v1.3.rst
@@ -273,9 +273,21 @@ Changelog
 :mod:`sklearn.linear_model`
 ...........................
 
-- |Enhancement| :class:`SGDClassifier`, :class:`SGDRegressor` and
-  :class:`SGDOneClassSVM` now preserve dtype for `numpy.float32`.
-  :pr:`25587` by :user:`Omar Salman <OmarManzoor>`
+- |Enhancement| :class:`linear_model.SGDClassifier`,
+  :class:`linear_model.SGDRegressor` and :class:`linear_model.SGDOneClassSVM`
+  now preserve dtype for `numpy.float32`.
+  :pr:`25587` by :user:`Omar Salman <OmarManzoor>`.
+
+- |API| Deprecates `n_iter` in favor of `max_iter` in
+  :class:`linear_model.BayesianRidge` and :class:`linear_model.ARDRegression`.
+  `n_iter` will be removed in scikit-learn 1.5. This change makes those
+  estimators consistent with the rest of estimators.
+  :pr:`25697` by :user:`John Pangas <jpangas>`.
+
+- |Enhancement| The `n_iter_` attribute has been included in 
+  :class:`linear_model.ARDRegression` to expose the actual number of iterations 
+  required to reach the stopping criterion.
+  :pr:`25697` by :user:`John Pangas <jpangas>`.
 
 :mod:`sklearn.metrics`
 ......................

diff --git a/sklearn/linear_model/_bayes.py b/sklearn/linear_model/_bayes.py
@@ -5,6 +5,7 @@
 # Authors: V. Michel, F. Pedregosa, A. Gramfort
 # License: BSD 3 clause
 
+import warnings
 from math import log
 from numbers import Integral, Real
 import numpy as np
@@ -15,7 +16,49 @@
 from ..utils.extmath import fast_logdet
 from scipy.linalg import pinvh
 from ..utils.validation import _check_sample_weight
-from ..utils._param_validation import Interval
+from ..utils._param_validation import Interval, Hidden, StrOptions
+
+
+# TODO(1.5) Remove
+def _deprecate_n_iter(n_iter, max_iter):
+    """Deprecates n_iter in favour of max_iter. Checks if the n_iter has been
+    used instead of max_iter and generates a deprecation warning if True.
+
+    Parameters
+    ----------
+    n_iter : int,
+        Value of n_iter attribute passed by the estimator.
+
+    max_iter : int, default=None
+        Value of max_iter attribute passed by the estimator.
+        If `None`, it corresponds to `max_iter=300`.
+
+    Returns
+    -------
+    max_iter : int,
+        Value of max_iter which shall further be used by the estimator.
+
+    Notes
+    -----
+    This function should be completely removed in 1.5.
+    """
+    if n_iter != "deprecated":
+        if max_iter is not None:
+            raise ValueError(
+                "Both `n_iter` and `max_iter` attributes were set. Attribute"
+                " `n_iter` was deprecated in version 1.3 and will be removed in"
+                " 1.5. To avoid this error, only set the `max_iter` attribute."
+            )
+        warnings.warn(
+            "'n_iter' was renamed to 'max_iter' in version 1.3 and "
+            "will be removed in 1.5",
+            FutureWarning,
+        )
+        max_iter = n_iter
+    elif max_iter is None:
+        max_iter = 300
+    return max_iter
+
 
 ###############################################################################
 # BayesianRidge regression
@@ -32,8 +75,12 @@ class BayesianRidge(RegressorMixin, LinearModel):
 
     Parameters
     ----------
-    n_iter : int, default=300
-        Maximum number of iterations. Should be greater than or equal to 1.
+    max_iter : int, default=None
+        Maximum number of iterations over the complete dataset before
+        stopping independently of any early stopping criterion. If `None`, it
+        corresponds to `max_iter=300`.
+
+        .. versionchanged:: 1.3
 
     tol : float, default=1e-3
         Stop the algorithm if w has converged.
@@ -83,14 +130,21 @@ class BayesianRidge(RegressorMixin, LinearModel):
     verbose : bool, default=False
         Verbose mode when fitting the model.
 
+    n_iter : int
+        Maximum number of iterations. Should be greater than or equal to 1.
+
+        .. deprecated:: 1.3
+           `n_iter` is deprecated in 1.3 and will be removed in 1.5. Use
+           `max_iter` instead.
+
     Attributes
     ----------
     coef_ : array-like of shape (n_features,)
         Coefficients of the regression model (mean of distribution)
 
     intercept_ : float
         Independent term in decision function. Set to 0.0 if
-        ``fit_intercept = False``.
+        `fit_intercept = False`.
 
     alpha_ : float
        Estimated precision of the noise.
@@ -162,7 +216,7 @@ class BayesianRidge(RegressorMixin, LinearModel):
     """
 
     _parameter_constraints: dict = {
-        "n_iter": [Interval(Integral, 1, None, closed="left")],
+        "max_iter": [Interval(Integral, 1, None, closed="left"), None],
         "tol": [Interval(Real, 0, None, closed="neither")],
         "alpha_1": [Interval(Real, 0, None, closed="left")],
         "alpha_2": [Interval(Real, 0, None, closed="left")],
@@ -174,12 +228,16 @@ class BayesianRidge(RegressorMixin, LinearModel):
         "fit_intercept": ["boolean"],
         "copy_X": ["boolean"],
         "verbose": ["verbose"],
+        "n_iter": [
+            Interval(Integral, 1, None, closed="left"),
+            Hidden(StrOptions({"deprecated"})),
+        ],
     }
 
     def __init__(
         self,
         *,
-        n_iter=300,
+        max_iter=None,  # TODO(1.5): Set to 300
         tol=1.0e-3,
         alpha_1=1.0e-6,
         alpha_2=1.0e-6,
@@ -191,8 +249,9 @@ def __init__(
         fit_intercept=True,
         copy_X=True,
         verbose=False,
+        n_iter="deprecated",  # TODO(1.5): Remove
     ):
-        self.n_iter = n_iter
+        self.max_iter = max_iter
         self.tol = tol
         self.alpha_1 = alpha_1
         self.alpha_2 = alpha_2
@@ -204,6 +263,7 @@ def __init__(
         self.fit_intercept = fit_intercept
         self.copy_X = copy_X
         self.verbose = verbose
+        self.n_iter = n_iter
 
     def fit(self, X, y, sample_weight=None):
         """Fit the model.
@@ -228,6 +288,8 @@ def fit(self, X, y, sample_weight=None):
         """
         self._validate_params()
 
+        max_iter = _deprecate_n_iter(self.n_iter, self.max_iter)
+
         X, y = self._validate_data(X, y, dtype=[np.float64, np.float32], y_numeric=True)
 
         if sample_weight is not None:
@@ -274,7 +336,7 @@ def fit(self, X, y, sample_weight=None):
         eigen_vals_ = S**2
 
         # Convergence loop of the bayesian ridge regression
-        for iter_ in range(self.n_iter):
+        for iter_ in range(max_iter):
 
             # update posterior mean coef_ based on alpha_ and lambda_ and
             # compute corresponding rmse
@@ -430,8 +492,10 @@ class ARDRegression(RegressorMixin, LinearModel):
 
     Parameters
     ----------
-    n_iter : int, default=300
-        Maximum number of iterations.
+    max_iter : int, default=None
+        Maximum number of iterations. If `None`, it corresponds to `max_iter=300`.
+
+        .. versionchanged:: 1.3
 
     tol : float, default=1e-3
         Stop the algorithm if w has converged.
@@ -470,6 +534,13 @@ class ARDRegression(RegressorMixin, LinearModel):
     verbose : bool, default=False
         Verbose mode when fitting the model.
 
+    n_iter : int
+        Maximum number of iterations.
+
+        .. deprecated:: 1.3
+           `n_iter` is deprecated in 1.3 and will be removed in 1.5. Use
+           `max_iter` instead.
+
     Attributes
     ----------
     coef_ : array-like of shape (n_features,)
@@ -487,6 +558,11 @@ class ARDRegression(RegressorMixin, LinearModel):
     scores_ : float
         if computed, value of the objective function (to be maximized)
 
+    n_iter_ : int
+        The actual number of iterations to reach the stopping criterion.
+
+        .. versionadded:: 1.3
+
     intercept_ : float
         Independent term in decision function. Set to 0.0 if
         ``fit_intercept = False``.
@@ -542,7 +618,7 @@ class ARDRegression(RegressorMixin, LinearModel):
     """
 
     _parameter_constraints: dict = {
-        "n_iter": [Interval(Integral, 1, None, closed="left")],
+        "max_iter": [Interval(Integral, 1, None, closed="left"), None],
         "tol": [Interval(Real, 0, None, closed="left")],
         "alpha_1": [Interval(Real, 0, None, closed="left")],
         "alpha_2": [Interval(Real, 0, None, closed="left")],
@@ -553,12 +629,16 @@ class ARDRegression(RegressorMixin, LinearModel):
         "fit_intercept": ["boolean"],
         "copy_X": ["boolean"],
         "verbose": ["verbose"],
+        "n_iter": [
+            Interval(Integral, 1, None, closed="left"),
+            Hidden(StrOptions({"deprecated"})),
+        ],
     }
 
     def __init__(
         self,
         *,
-        n_iter=300,
+        max_iter=None,  # TODO(1.5): Set to 300
         tol=1.0e-3,
         alpha_1=1.0e-6,
         alpha_2=1.0e-6,
@@ -569,8 +649,9 @@ def __init__(
         fit_intercept=True,
         copy_X=True,
         verbose=False,
+        n_iter="deprecated",  # TODO(1.5): Remove
     ):
-        self.n_iter = n_iter
+        self.max_iter = max_iter
         self.tol = tol
         self.fit_intercept = fit_intercept
         self.alpha_1 = alpha_1
@@ -581,6 +662,7 @@ def __init__(
         self.threshold_lambda = threshold_lambda
         self.copy_X = copy_X
         self.verbose = verbose
+        self.n_iter = n_iter
 
     def fit(self, X, y):
         """Fit the model according to the given training data and parameters.
@@ -603,6 +685,8 @@ def fit(self, X, y):
 
         self._validate_params()
 
+        max_iter = _deprecate_n_iter(self.n_iter, self.max_iter)
+
         X, y = self._validate_data(
             X, y, dtype=[np.float64, np.float32], y_numeric=True, ensure_min_samples=2
         )
@@ -648,7 +732,7 @@ def update_coeff(X, y, coef_, alpha_, keep_lambda, sigma_):
             else self._update_sigma_woodbury
         )
         # Iterative procedure of ARDRegression
-        for iter_ in range(self.n_iter):
+        for iter_ in range(max_iter):
             sigma_ = update_sigma(X, alpha_, lambda_, keep_lambda)
             coef_ = update_coeff(X, y, coef_, alpha_, keep_lambda, sigma_)
 
@@ -688,6 +772,8 @@ def update_coeff(X, y, coef_, alpha_, keep_lambda, sigma_):
             if not keep_lambda.any():
                 break
 
+        self.n_iter_ = iter_ + 1
+
         if keep_lambda.any():
             # update sigma and mu using updated params from the last iteration
             sigma_ = update_sigma(X, alpha_, lambda_, keep_lambda)

diff --git a/sklearn/linear_model/tests/test_bayes.py b/sklearn/linear_model/tests/test_bayes.py
@@ -73,7 +73,7 @@ def test_bayesian_ridge_score_values():
         alpha_2=alpha_2,
         lambda_1=lambda_1,
         lambda_2=lambda_2,
-        n_iter=1,
+        max_iter=1,
         fit_intercept=False,
         compute_score=True,
     )
@@ -174,7 +174,7 @@ def test_update_of_sigma_in_ard():
     # of the ARDRegression algorithm. See issue #10128.
     X = np.array([[1, 0], [0, 0]])
     y = np.array([0, 0])
-    clf = ARDRegression(n_iter=1)
+    clf = ARDRegression(max_iter=1)
     clf.fit(X, y)
     # With the inputs above, ARDRegression prunes both of the two coefficients
     # in the first iteration. Hence, the expected shape of `sigma_` is (0, 0).
@@ -292,3 +292,33 @@ def test_dtype_correctness(Estimator):
     coef_32 = model.fit(X.astype(np.float32), y).coef_
     coef_64 = model.fit(X.astype(np.float64), y).coef_
     np.testing.assert_allclose(coef_32, coef_64, rtol=1e-4)
+
+
+# TODO(1.5) remove
+@pytest.mark.parametrize("Estimator", [BayesianRidge, ARDRegression])
+def test_bayesian_ridge_ard_n_iter_deprecated(Estimator):
+    """Check the deprecation warning of `n_iter`."""
+    depr_msg = (
+        "'n_iter' was renamed to 'max_iter' in version 1.3 and will be removed in 1.5"
+    )
+    X, y = diabetes.data, diabetes.target
+    model = Estimator(n_iter=5)
+
+    with pytest.warns(FutureWarning, match=depr_msg):
+        model.fit(X, y)
+
+
+# TODO(1.5) remove
+@pytest.mark.parametrize("Estimator", [BayesianRidge, ARDRegression])
+def test_bayesian_ridge_ard_max_iter_and_n_iter_both_set(Estimator):
+    """Check that a ValueError is raised when both `max_iter` and `n_iter` are set."""
+    err_msg = (
+        "Both `n_iter` and `max_iter` attributes were set. Attribute"
+        " `n_iter` was deprecated in version 1.3 and will be removed in"
+        " 1.5. To avoid this error, only set the `max_iter` attribute."
+    )
+    X, y = diabetes.data, diabetes.target
+    model = Estimator(n_iter=5, max_iter=5)
+
+    with pytest.raises(ValueError, match=err_msg):
+        model.fit(X, y)