can't find the inplace operation: one of the variables needed for gradient computation has been modified by an inplace operation

Question

I am trying to compute a loss on the jacobian of the network (i.e. to perform double backprop), and I get the following error: RuntimeError: one of the variables needed for

Answer 1

grad_output.zero_() is in-place and so is grad_output[:, i-1] = 0. In-place means "modify a tensor instead of returning a new one, which has the modifications applied". An example solution which is not in-place is torch.where. An example use to zero out the 1st column

import torch
t = torch.randn(3, 3)
ixs = torch.arange(3, dtype=torch.int64)
zeroed = torch.where(ixs[None, :] == 1, torch.tensor(0.), t)

zeroed
tensor([[-0.6616,  0.0000,  0.7329],
        [ 0.8961,  0.0000, -0.1978],
        [ 0.0798,  0.0000, -1.2041]])

t
tensor([[-0.6616, -1.6422,  0.7329],
        [ 0.8961, -0.9623, -0.1978],
        [ 0.0798, -0.7733, -1.2041]])

Notice how t retains the values it had before and zeroed has the values you want.