If I want to compute backprop with some element of output from model:

```
output = model(image) # tensor([[0.6000], [0.2000], [0.1500], [0.0500]])
mask = output >= 0.2 # tensor([[ True], [ True], [False], [False]])
predict = output[mask] # tensor([0.6000, 0.2000])
loss = criterion(predict, ground_truth[mask]) # some number
optim.zero_grad()
loss.backward()
```

In the example above, assume that I am dealing with the binary classification with the batch size is 4 and I only want to compute the gradient from which output is greater or equal to 0.2. So my question, Is it the correct way to do it, if not please let me know how, thank you.