# -*- coding: utf-8 -*-
# numpytest3.py 

import numpy as np
import statistics
import matplotlib.pyplot as plt

x = np.linspace(1, 30, 30, endpoint = True) 
n = len(x)
y = 2+3*x + np.random.normal(size=n, loc=0, scale=10)
mx = statistics.mean(x);  my = statistics.mean(y)

b1 = (sum(x*y) - n* mx * my ) / (sum(x ** 2) - n* mx **2)
b0 = my - b1 * mx
yhat = b0 + b1 * x

b0 = round(b0, 3); b1 = round(b1, 3)

print('회귀식은 : y= {0} + {1} x 입니다.'.format(b0, b1))

plt.plot(x, y, '*') 
plt.plot(x, yhat)
plt.text(20, 35,s='y= {0} + {1} x'.format(b0, b1) )
plt.xlim(-0.5, 30.5)