fixed a corner case when ||g(x_0)|| is exactly zero

fixed a corner case when ||g(x_0)|| is exactly zero

Update README.md

removed unused struct

Delete .vscode directory

remove unused retval, add bounded levelset in comments

use inf norm for better precision control

Update lbfgs.hpp

Update lbfgs.hpp

Update README.md

Update README.md

Update README.md

Update README.md

Update README.md

Update README.md