How to use L-BFGS in the C++ LibTorch?

C++
1

Hi!

How to use L-BFGS in the C++ LibTorch?
Particularly, how to implement “closure function” in C++?

Would you please offer an example using L-BFGS?

Thank you!

3 
torch::optim::LBFGS optimizer = ... // init
auto closure = [&](){
    optimizer.zero_grad();
    // must call model forward inside, and then calculate loss
    torch::Tensor out = model->forward(...);
    torch::Tensor loss = loss_func(out,...);
    loss.backward();
    return loss;
};
optimizer.step(closure);