Pytorch. Can Autograd Be Used When The Final Tensor Has More Than A Single Value In It?

Can autograd be used when the final tensor has more than a single value in it? I tried the following. x = torch.tensor([4.0, 5.0], requires_grad=True) y = x ** 2 print(y) y.back

Solution 1:

See https://pytorch.org/tutorials/beginner/blitz/autograd_tutorial.html#gradients

y.backward() is same as y.backward(torch.tensor(1.0))

Usually, the output is scalar and hence the scalar is passed to backward as a default choice. However, since your output is two dimensional you should call y.backward(torch.tensor([1.0,1.0]))

This will give expected results with x.grad being tensor([ 8., 10.])