Solved by ptrblck in post #2 
              
              
                These should be the ids of the parameters. 
This small code snippet demonstrates this behavior: 
x = torch.randn(10, requires_grad=True)
x_id = id(x)

y = torch.randn(10, requires_grad=True)

optimizer = torch.optim.Adam([x, y], lr=1.)

param_id = optimizer.state_dict()['param_groups'][0]['params'][…