This is a nice introduction, but it looks there is a problem with the formatting: some of the math is not rendered properly (in the source, some expressions are wrapped in dollar-signs rather than script tags).
Gonum has an LBFGS implementation <a href="https://github.com/gonum/optimize/blob/master/lbfgs.go" rel="nofollow">https://github.com/gonum/optimize/blob/master/lbfgs.go</a>