tensorflow_example/Day_02_04_cost.py at master · pyotel/tensorflow_example

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# Day_02_04_cost.py

import matplotlib.pyplot as plt

def cost(y, x, a, b):

c = 0

for i in range(len(y)):

yhat = a * x[i] + b

c += (y[i] - yhat) ** 2

return c/len(y)

def gradient_descent(y, x, a):

c = 0

for i in range(len(y)):

# c += (a*x[i] - y[i]) ** 2

c += 2 * (a * x[i] - y[i]) * x[i]

return c/len(y)

# a = 1, b = 0

x = [1, 2, 3, 4, 5]

y = [1, 2, 3, 4, 5]

xx, yy = [], []

for i in range(-30, 50, 1):

# print(i/10)

c = cost(y, x, i/10, 0)

print(i/10, c)

xx.append(i/10)

yy.append(c)

# plt.plot(xx, yy, 'ro')

# plt.show()

# 미분 : 순간변화량

# y = x 1

# y = 2x 2

# y = 3 0

# y = x^2 2x

# y = (x-3)^2 2(x-3)

print('-'*50)

a = -10

for i in range(100):

c = cost(y, x, a, 0)

grad = gradient_descent(y, x, a)

a -= grad * 0.01

print('{:.6f} : {:.6f} {}'.format(a, grad, c))

p1 = 20

print(a*p1)

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