Solved by Ranahanocka in post #15 
              
              
                It’s actually from the torch.optim package (you can see all the optimizers here, in addition to SGD, Adam, there’s also LBFGS, and more…) 
https://pytorch.org/docs/stable/optim.html 
To use LBFGS, your optimizer would be: 
optimizer = optim.LBFGS