Source code for skpoly._legendre

import numpy as np
from numpy.polynomial.legendre import legvander

from ._base import _BasePolynomialBasisTransformer




class LegendreFeatures(_BasePolynomialBasisTransformer):
    """Generate Legendre polynomial features.

    Parameters
    ----------
    degree : int, default=3
        Highest degree of the basis.
    feature_range : tuple of float, default=(0.0, 1.0)
        Interval ``[a, b]`` that bounds the input features.
    include_bias : bool, default=False
        If ``True``, include the constant Legendre polynomial.
    tensor_product : bool, default=False
        If ``True``, append tensor product features for each pair of columns.

    Attributes
    ----------
    n_features_in_ : int
        Number of features in the input passed to :meth:`fit`.
    feature_range_ : tuple of float
        Validated feature range.
    n_output_features_ : int
        Total number of output features generated by :meth:`transform`.
    """

    def _setup(self) -> None:
        return None

    def _scale_to_basis(self, X: np.ndarray) -> np.ndarray:
        lower, upper = self.feature_range_
        span = upper - lower
        scaled = ((X - lower) * 2.0 / span) - 1.0
        return np.clip(scaled, -1.0, 1.0, out=scaled)

    def _evaluate_basis(self, X: np.ndarray) -> np.ndarray:
        if X.shape[1] == 0:
            return np.empty((X.shape[0], 0, self.degree + 1), dtype=np.float64)
        return legvander(X, self.degree)



__all__ = ["LegendreFeatures"]