#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Kleinste-kwadraten lijnpassen met numpy.polyfit.
Hoofdstuk: 78/79 — Lijnpassen (least squares)
Vereist: numpy (pip install numpy)
"""
import numpy as np
rng = np.random.default_rng(42)
x = np.linspace(0, 10, 21)
y = 2.0 * x + 1.0 + rng.normal(0, 0.6, size=x.size)
a, b = np.polyfit(x, y, 1)
y_fit = a * x + b
residuen = y - y_fit
print(f"Fit: y = {a:.3f} * x + {b:.3f}")
print("Gemiddelde residu:", np.mean(residuen))
print("Standaardafwijking residu:", np.std(residuen, ddof=1))