How to apply layer-wise learning rate in Pytorch?

Here is the solution:

from torch.optim import Adam

model = Net()

optim = Adam(
    [
        {"params": model.fc.parameters(), "lr": 1e-3},
        {"params": model.agroupoflayer.parameters()},
        {"params": model.lastlayer.parameters(), "lr": 4e-2},
    ],
    lr=5e-4,
)

Other parameters that are didn’t specify in optimizer will not optimize. So you should state all layers or groups(OR the layers you want to optimize). and if you didn’t specify the learning rate it will take the global learning rate(5e-4).
The trick is when you create the model you should give names to the layers or you can group it.