dwarfplanetsfactory 0.0.3

Dwarf planet factory — classify, build and catalogue dwarf planets of any type: Kuiper belt, scattered disk, plutino, cold classical, detached, binary, Ceres-type, and sednoid.
Documentation 
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use crate::config::parameters;

/// Check if a body is in a mean-motion resonance p:q with Neptune
/// by comparing its semi-major axis with the expected resonant a.
pub fn resonance_semi_major_axis(p: u32, q: u32) -> f64 {
    if p == 0 || q == 0 {
        return 0.0;
    }
    let ratio = (q as f64) / (p as f64);
    parameters::NEPTUNE_A * ratio.powf(2.0 / 3.0)
}

/// Returns true if semi_major_au is within tolerance of the p:q
/// Neptune resonance location.
pub fn is_near_resonance(semi_major_au: f64, p: u32, q: u32, tolerance_au: f64) -> bool {
    let a_res = resonance_semi_major_axis(p, q);
    (semi_major_au - a_res).abs() < tolerance_au
}

/// Resonance width estimate (AU) — first-order resonance
/// Δa ≈ a_res * (m_Neptune/m_Sun * e)^(1/2) for first-order
pub fn resonance_width(p: u32, q: u32, eccentricity: f64) -> f64 {
    let a_res = resonance_semi_major_axis(p, q);
    let mass_ratio = parameters::NEPTUNE_MASS / parameters::SOLAR_MASS;
    a_res * (mass_ratio * eccentricity.abs().max(0.001)).sqrt()
}

/// Libration timescale (years) — approximate
pub fn libration_period_years(p: u32, q: u32, eccentricity: f64) -> f64 {
    let a_res = resonance_semi_major_axis(p, q);
    let t_orb = parameters::orbital_period(a_res, parameters::SOLAR_MASS) / parameters::YEAR;
    let mass_ratio = parameters::NEPTUNE_MASS / parameters::SOLAR_MASS;
    if mass_ratio < 1.0e-20 || eccentricity < 1.0e-10 {
        return f64::INFINITY;
    }
    t_orb / (mass_ratio * eccentricity).sqrt()
}

/// Known major Neptune resonances and their approximate semi-major axes
pub fn major_resonances() -> Vec<(u32, u32, f64)> {
    let resonances = [(2, 3), (1, 2), (3, 5), (4, 7), (2, 5), (1, 3)];
    resonances
        .iter()
        .map(|&(p, q)| (p, q, resonance_semi_major_axis(p, q)))
        .collect()
}

/// Identify the closest Neptune resonance within tolerance
pub fn closest_resonance(semi_major_au: f64, tolerance_au: f64) -> Option<(u32, u32, f64)> {
    major_resonances()
        .into_iter()
        .filter(|&(_, _, a_res)| (semi_major_au - a_res).abs() < tolerance_au)
        .min_by(|a, b| {
            (semi_major_au - a.2)
                .abs()
                .partial_cmp(&(semi_major_au - b.2).abs())
                .unwrap_or(std::cmp::Ordering::Equal)
        })
}