ENH: #455 Make IdentityLibrary a subclass of Polynomial Library

pysindy/feature_library/__init__.py

@@ -3,9 +3,9 @@
 from .custom_library import CustomLibrary
 from .fourier_library import FourierLibrary
 from .generalized_library import GeneralizedLibrary
-from .identity_library import IdentityLibrary
 from .parameterized_library import ParameterizedLibrary
 from .pde_library import PDELibrary
+from .polynomial_library import IdentityLibrary
 from .polynomial_library import PolynomialLibrary
 from .sindy_pi_library import SINDyPILibrary
 from .weak_pde_library import WeakPDELibrary

pysindy/feature_library/polynomial_library.py

@@ -282,3 +282,33 @@ def n_poly_features(
         else:
             n_feat += comb(n_in_feat + deg - 1, deg)
     return n_feat
+
+
+def IdentityLibrary():
+    """
+    Generate an identity library which maps all input features to
+    themselves.
+
+    Attributes
+    ----------
+    n_features_in_ : int
+        The total number of input features.
+
+    n_output_features_ : int
+        The total number of output features. The number of output features
+        is equal to the number of input features.
+
+    Examples
+    --------
+    >>> import numpy as np
+    >>> from pysindy.feature_library import IdentityLibrary
+    >>> x = np.array([[0,-1],[0.5,-1.5],[1.,-2.]])
+    >>> lib = IdentityLibrary().fit(x)
+    >>> lib.transform(x)
+    array([[ 0. , -1. ],
+           [ 0.5, -1.5],
+           [ 1. , -2. ]])
+    >>> lib.get_feature_names()
+    ['x0', 'x1']
+    """
+    return PolynomialLibrary(degree=1, include_bias=False)

test/test_feature_library.py

@@ -224,11 +224,9 @@ def test_sindypi_library_bad_params(params):
 @pytest.mark.parametrize(
     "library",
     [
-        IdentityLibrary(),
         PolynomialLibrary(),
         PolynomialLibrary(include_bias=False),
         FourierLibrary(),
-        IdentityLibrary() + PolynomialLibrary(),
         pytest.lazy_fixture("custom_library"),
         pytest.lazy_fixture("custom_library_bias"),
         pytest.lazy_fixture("generalized_library"),
@@ -246,11 +244,9 @@ def test_fit_transform(data_lorenz, library):
 @pytest.mark.parametrize(
     "library",
     [
-        IdentityLibrary(),
         PolynomialLibrary(),
         PolynomialLibrary(include_bias=False),
         FourierLibrary(),
-        IdentityLibrary() + PolynomialLibrary(),
         pytest.lazy_fixture("custom_library"),
         pytest.lazy_fixture("custom_library_bias"),
         pytest.lazy_fixture("generalized_library"),
@@ -269,10 +265,8 @@ def test_change_in_data_shape(data_lorenz, library):
 @pytest.mark.parametrize(
     "library, shape",
     [
-        (IdentityLibrary(), 3),
         (PolynomialLibrary(include_bias=False), 9),
         (PolynomialLibrary(), 10),
-        (IdentityLibrary() + PolynomialLibrary(), 13),
         (FourierLibrary(), 6),
         (pytest.lazy_fixture("custom_library_bias"), 13),
         (pytest.lazy_fixture("custom_library"), 12),
@@ -292,7 +286,6 @@ def test_output_shape(data_lorenz, library, shape):
 @pytest.mark.parametrize(
     "library",
     [
-        IdentityLibrary(),
         PolynomialLibrary(),
         PolynomialLibrary(include_bias=False),
         FourierLibrary(),
@@ -410,7 +403,6 @@ def test_tensored(data_lorenz):
 @pytest.mark.parametrize(
     "library",
     [
-        IdentityLibrary(),
         PolynomialLibrary(),
         FourierLibrary(),
         PolynomialLibrary() + FourierLibrary(),