pytorch tensor 套 tensor需要cat

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import torch
a = torch.tensor(0.0)
b = torch.tensor(0.0)

a.requires_grad = True
b.requires_grad = True

cosa = torch.cos(a)
cosb = torch.cos(b)

y1 = cosa + cosb
y2 = torch.tensor([
    cosa, cosb
])

y2.sum().backward()  # RuntimeError: element 0 of tensors does not require grad and does not have a grad_fn

print("a has grad ", a.requires_grad)
print("a grad", a.grad)

要应该拼接起来

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y2 = torch.cat([
    cosa, cosb
], dim=0)