pub trait VelIntegrates<R: Real, S: VectorSpace<R>> {
// Required method
fn step_with_vel(
&self,
time: R,
state: &mut [S],
dt: R,
vel: &'_ dyn Fn(R, S) -> S,
force: &'_ dyn Fn(R, S) -> S,
) -> S;
// Provided method
fn init_with_vel(
&self,
state: S,
_dt: R,
_vel: &'_ dyn Fn(R, S) -> S,
_force: &'_ dyn Fn(R, S) -> S,
) -> Box<[S]> { ... }
}