Function stradv 

pub fn stradv(
    q: f64,
    r: &mut Vec3,
    v: &mut Vec3,
    rad: f64,
    acc: f64,
    smax: f64,
) -> f64

stradv advances a particle of given position and velocity until it reaches a specified radius. It then returns with updated position and velocity. It is up to the user not to request a value that cannot be reached.

Arguments:

• q: mass ratio = M2/M1
• r: Initial and final position
• v: Initial and final velocity
• rad: Radius to aim for
• acc: Accuracy with which to place output point at rad.
• smax: Largest time step allowed. It is possible that the routine could take such a large step that it misses the point when the stream is inside the requested radius. This allows one to control this. Typical value = 1.e-3.

Returns:

• time step taken