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Diffstat (limited to 'rand/src/distributions/unit_sphere.rs')
-rw-r--r-- | rand/src/distributions/unit_sphere.rs | 99 |
1 files changed, 0 insertions, 99 deletions
diff --git a/rand/src/distributions/unit_sphere.rs b/rand/src/distributions/unit_sphere.rs deleted file mode 100644 index 37de88b..0000000 --- a/rand/src/distributions/unit_sphere.rs +++ /dev/null @@ -1,99 +0,0 @@ -// Copyright 2018 Developers of the Rand project. -// -// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or -// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license -// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your -// option. This file may not be copied, modified, or distributed -// except according to those terms. - -use Rng; -use distributions::{Distribution, Uniform}; - -/// Samples uniformly from the surface of the unit sphere in three dimensions. -/// -/// Implemented via a method by Marsaglia[^1]. -/// -/// -/// # Example -/// -/// ``` -/// use rand::distributions::{UnitSphereSurface, Distribution}; -/// -/// let sphere = UnitSphereSurface::new(); -/// let v = sphere.sample(&mut rand::thread_rng()); -/// println!("{:?} is from the unit sphere surface.", v) -/// ``` -/// -/// [^1]: Marsaglia, George (1972). [*Choosing a Point from the Surface of a -/// Sphere.*](https://doi.org/10.1214/aoms/1177692644) -/// Ann. Math. Statist. 43, no. 2, 645--646. -#[derive(Clone, Copy, Debug)] -pub struct UnitSphereSurface; - -impl UnitSphereSurface { - /// Construct a new `UnitSphereSurface` distribution. - #[inline] - pub fn new() -> UnitSphereSurface { - UnitSphereSurface - } -} - -impl Distribution<[f64; 3]> for UnitSphereSurface { - #[inline] - fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> [f64; 3] { - let uniform = Uniform::new(-1., 1.); - loop { - let (x1, x2) = (uniform.sample(rng), uniform.sample(rng)); - let sum = x1*x1 + x2*x2; - if sum >= 1. { - continue; - } - let factor = 2. * (1.0_f64 - sum).sqrt(); - return [x1 * factor, x2 * factor, 1. - 2.*sum]; - } - } -} - -#[cfg(test)] -mod tests { - use distributions::Distribution; - use super::UnitSphereSurface; - - /// Assert that two numbers are almost equal to each other. - /// - /// On panic, this macro will print the values of the expressions with their - /// debug representations. - macro_rules! assert_almost_eq { - ($a:expr, $b:expr, $prec:expr) => ( - let diff = ($a - $b).abs(); - if diff > $prec { - panic!(format!( - "assertion failed: `abs(left - right) = {:.1e} < {:e}`, \ - (left: `{}`, right: `{}`)", - diff, $prec, $a, $b)); - } - ); - } - - #[test] - fn norm() { - let mut rng = ::test::rng(1); - let dist = UnitSphereSurface::new(); - for _ in 0..1000 { - let x = dist.sample(&mut rng); - assert_almost_eq!(x[0]*x[0] + x[1]*x[1] + x[2]*x[2], 1., 1e-15); - } - } - - #[test] - fn value_stability() { - let mut rng = ::test::rng(2); - let dist = UnitSphereSurface::new(); - assert_eq!(dist.sample(&mut rng), - [-0.24950027180862533, -0.7552572587896719, 0.6060825747478084]); - assert_eq!(dist.sample(&mut rng), - [0.47604534507233487, -0.797200864987207, -0.3712837328763685]); - assert_eq!(dist.sample(&mut rng), - [0.9795722330927367, 0.18692349236651176, 0.07414747571708524]); - } -} |