Is var[0,:] unpacking for using autograd based backprop or not?

Hello guys. According to this link, If we want to implement a loss function using autograd concept, we should not use unpacking variables. Something like this is forbidden in autograd based backprop:[0,:]

I would like to know is var[0,:] unpacking as same as[0,:]? (var is a variable type)

Indexing variables is fine. So you can do var[0, :] without a problem

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Thanks for your response, But as you have mentioned, I did following code:

output = net(images)  # batches*95*S*S
for ind in range(B):
     output[:,2+(1+coords)*ind,:,:] = torch.sqrt(output[:,2+(1+coords)*ind,:,:])
     output[:,3+(1+coords)*ind,:,:] = torch.sqrt(output[:,3+(1+coords)*ind,:,:])

But bellow error occurred:

Traceback (most recent call last):
File “”, line 200, in
File “”, line 193, in train
File “/home/mohammad/anaconda3/lib/python3.5/site-packages/torch/autograd/”, line 146, in backward
self._execution_engine.run_backward((self,), (gradient,), retain_variables)
File “/home/mohammad/anaconda3/lib/python3.5/site-packages/torch/autograd/_functions/”, line 130, in backward
i, = self.saved_tensors
RuntimeError: one of the variables needed for gradient computation has been modified by an inplace operation

Could you please tell me what is the problem?

Just to confirm, what is your pytorch version? (run torch.__version__ in the python interpreter).
One thing, tensor assignment is an inplace operation, so that might indicate where the problem is.

My torch version is: 0.1.11+b13b701.

So Is there any way to manipulate some parts of my output variable and avoid this error? Because as you can see in My loss function, I should take square of some parts of output variable!

The problem seems to be that you are trying to apply an in-place operation that can’t be in-place because the backprop wouldn’t work (sqrt).

First idea that I had was to perform the operations out of place in different tensors and then concatenate them, something like

out1 = output[:, 2::1+coords, :, :].sqrt()
out2 = output[:, 3::1+coords, :, :].sqrt()

but that still requires concatenating and shuffling around the elements in the tensor, which doesn’t sound like a good solution.

I have no better ideas now given the information I have about what you want to do, sorry

Thanks for your recommendation. I will try that.