import torch
from torch.autograd import Variable

# 变量

x = Variable(torch.ones(2, 2), requires_grad=True)
print(x)

y = x + 2
print(y)

z = y * y * 3
out = z.mean()
print(z)
print(out)

# 梯度

out.backward()
print(x.grad)

a = torch.randn(3)
a = Variable(a, requires_grad=True)
b = a * 2
while b.data.norm() < 1000:
    b = b * 2
print(b)

gradients = torch.FloatTensor([0.1, 1.0, 0.0001])
b.backward(gradients)
print(a.grad)