import matplotlib.pyplot as plt
x_axix = np.arange(1, 256, 1)
y = []
for t in x_axix:
    y_1 = 1 / (1 + math.exp(-t))
    y.append(y_1)
plt.title('Result Analysis')
plt.plot(x_axix, y, color='yellow', label='sigmoid')
plt.plot(x_axix, l1, color='green', label='L1')
plt.plot(x_axix, l2, color='red', label='L2')
plt.plot(x_axix, ssim, color='skyblue', label='ssim') 
plt.legend()  #show the picture
plt.xlabel('iteration times')
plt.ylabel('rate')
plt.show()