Lagrange polynomial

lagrange_polynomial.py

class LagrangePolynomial:

    def __init__(self, x_points: list[float], y_points: list[float]) -> None:
        self.xs = x_points
        self.ys = y_points

    def _basis(self, x: float, j: int) -> float:
        """Lagrange basis polynomial l_j(x)"""
        x_j = self.xs[j]
        product = 1.0
        for x_m in self.xs:
            if x_m != x_j:
                product *= (x - x_m) / (x_j - x_m)
        return product

    def lagrange_poly(self, x: float) -> float:
        """Lagrange polynomial at x"""
        total = 0.0
        for j in range(len(self.ys)):
            total += self.ys[j] * self._basis(x, j)
        return total