Function GetIpoptDualInf 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn GetIpoptDualInf(
    ipopt_problem: IpoptProblem,
) -> Number

Final dual infeasibility (max gradient-of-Lagrangian norm) for the most recent solve.

Safety

ipopt_problem must be a valid IpoptProblem or NULL.