rust-roche 0.1.0

Rust translation of Tom Marsh's cpp-roche package for modelling Roche distorted stars/binary systems.
Documentation 
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use crate::{Vec3, Star};
use crate::{x_l1_1, x_l1_2, rpot1, rpot2};


///
/// ref_sphere computes the radius of a reference sphere just outside a Roche distorted star
/// along the line of centres and centred upon its centre of mass. This sphere, which is guaranteed
/// to enclose the equipotential in question can then be used to define regions for searching for 
/// equipotential crossing when computing eclipses. The Roche-distorted star is defined by the mass 
/// ratio and the (linear) filling factor defined as the distance from the centre of mass of the 
/// star to its surface in the direction of the L1 point divided by the distance to the L1 point. 
/// A filling factor = 1 is Roche filling. Note that the size of the Roche lobe is calculated as 
/// appropriate given any asynchronism.
///
/// \param q    the mass ratio = M2/M1
/// \param star specifies which star, primary or secondary is under consideration
/// \param spin ratio spin/orbital frequencies to allow for asynchronism
/// \param ffac linear filling factor.
/// \param rref radius of the reference sphere. This will be 0.1% expanded above the minimum
/// size to avoid round off bugs, if it remains within Roche lobe.
/// \param pref reference potential. Roche potential on surface of distorted star.
///
pub fn ref_sphere(q: f64, star: Star, spin: f64, ffac: f64) -> (f64, f64) {
    let tref: f64;
    let rref: f64;
    let pref: f64;
    if star == Star::Primary {
        tref = x_l1_1(q, spin);
        rref = tref * 1.0_f64.min(1.001*ffac);
        pref = rpot1(q, spin, &Vec3 { x: ffac*tref, y: 0.0, z: 0.0 });
        (rref, pref)
    } else if star == Star::Secondary {
        tref = 1.0 - x_l1_2(q, spin);
        rref = tref * 1.0_f64.min(1.001*ffac);
        pref = rpot2(q, spin, &Vec3 { x: 1.0 - ffac*tref, y: 0.0, z: 0.0 });
        (rref, pref)
    } else {
        panic!("star is not an instance of Star")
    }
}