Hi everybody,

I have an image and want to calculate loss just for 1 pixel on it, therefore I use a mask array and masked the other value that I want to be shown in the loss . my code is just below, but I got an error and I couldn’t fix it . just somebody can please help to know me whats wrong with my code?

```
fm = 64
net = nn.Sequential(
MaskedConv2d('A', 3, fm, 3, 1, 1, bias=False), nn.BatchNorm2d(fm), nn.ReLU(True),
MaskedConv2d('A', fm, fm, 3, 1, 1, bias=False), nn.BatchNorm2d(fm), nn.ReLU(True),
MaskedConv2d('A', fm, fm, 3, 1, 1, bias=False), nn.BatchNorm2d(fm), nn.ReLU(True),
MaskedConv2d('A', fm, fm, 3, 1, 1, bias=False), nn.BatchNorm2d(fm), nn.ReLU(True),
MaskedConv2d('A', fm, fm, 3, 1, 1, bias=False), nn.BatchNorm2d(fm), nn.ReLU(True),
MaskedConv2d('A', fm, fm, 3, 1, 1, bias=False), nn.BatchNorm2d(fm), nn.ReLU(True),
MaskedConv2d('A', fm, fm, 3, 1, 1, bias=False), nn.BatchNorm2d(fm), nn.ReLU(True),
MaskedConv2d('A', fm, fm, 3, 1, 1, bias=False), nn.BatchNorm2d(fm), nn.ReLU(True),
nn.Conv2d(fm, 3, 1))
sample = V(torch.zeros(bs, 3, picSize,picSize))
residual = V(torch.zeros(bs, 3, picSize, picSize))
res_mask = V(torch.zeros_like(residual.data))
for batch_idx, (images, labels) in enumerate(dataloaders):
images = V(images, requires_grad = False)
for i in range(picSize):
for j in range(picSize):
optimizer.zero_grad()
out = net(sample)
residual[:,:,i,j] = (images[:,:,i,j] - out[:,:,i,j])**2
res_mask = V(torch.zeros_like(residual.data))
res_mask[:,:,i,j] = 1
residual = torch.mul(residual,res_mask)
loss = (residual.sum()/(bs * 3))
pdb.set_trace()
loss.backward(retain_graph = True)
optimizer.step()
sample[:,:,i,j] = images[:,:,i,j]
```

Error: one of the variables needed for gradient computation has been modified by an inplace operation

@jpeg729