Function minimize 

pub fn minimize<F, G>(
    f: F,
    gradient: Option<G>,
    x: Vec<f64>,
    plan: &ObjectivePlan,
) -> Result<OptimizeResult, Error>
where
    F: FnMut(&[f64]) -> f64,
    G: Fn(&[f64], &mut [f64]),

Projected BFGS/trust-region objective minimization with acceptance ratio.