ex02.py

import numpy as np
import matplotlib.pyplot as plt

x_data = [1.0, 2.0, 3.0]
y_data = [2.0, 4.0, 6.0]

def foward(x):
    return x*w
def loss(x, y):
    return (x*w-y)**2

w_list = []
mse_list = []

for w in np.arange(0.0, 4.1, 0.1):
    print('w=', w)
    l_sum = 0
    for x_val, y_val in zip(x_data, y_data):
        y_pred_val = foward(x_val)
        loss_val = loss(x_val, y_val) #注
        l_sum += loss_val
        print('\t', x_val, y_val, y_pred_val)
    print('MSE=', l_sum / 3, '\n')
    w_list.append(w)
    mse_list.append(l_sum/len(x_data))


plt.plot(w_list, mse_list)
plt.xlabel('w')
plt.ylabel('MSE')
plt.show()


#You used the same name loss for:

#the function def loss(x, y): ...
#a variable inside the loop: loss = loss(x_val, y_val)

#This line redefines (overwrites) the name loss — so after the first iteration,
#loss is no longer a function, it’s just a float number.
#Then, on the next loop, when Python tries to do loss(x_val, y_val),
#it fails — because loss is now a number, not a callable function.