| // 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. |
| |
| #![allow(deprecated)] |
| #![allow(clippy::all)] |
| |
| use crate::Rng; |
| use crate::distributions::{Distribution, Uniform}; |
| |
| /// Samples uniformly from the edge of the unit circle in two dimensions. |
| /// |
| /// Implemented via a method by von Neumann[^1]. |
| /// |
| /// [^1]: von Neumann, J. (1951) [*Various Techniques Used in Connection with |
| /// Random Digits.*](https://mcnp.lanl.gov/pdf_files/nbs_vonneumann.pdf) |
| /// NBS Appl. Math. Ser., No. 12. Washington, DC: U.S. Government Printing |
| /// Office, pp. 36-38. |
| #[deprecated(since="0.7.0", note="moved to rand_distr crate")] |
| #[derive(Clone, Copy, Debug)] |
| pub struct UnitCircle; |
| |
| impl UnitCircle { |
| /// Construct a new `UnitCircle` distribution. |
| #[inline] |
| pub fn new() -> UnitCircle { |
| UnitCircle |
| } |
| } |
| |
| impl Distribution<[f64; 2]> for UnitCircle { |
| #[inline] |
| fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> [f64; 2] { |
| let uniform = Uniform::new(-1., 1.); |
| let mut x1; |
| let mut x2; |
| let mut sum; |
| loop { |
| x1 = uniform.sample(rng); |
| x2 = uniform.sample(rng); |
| sum = x1*x1 + x2*x2; |
| if sum < 1. { |
| break; |
| } |
| } |
| let diff = x1*x1 - x2*x2; |
| [diff / sum, 2.*x1*x2 / sum] |
| } |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| use crate::distributions::Distribution; |
| use super::UnitCircle; |
| |
| /// 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 = crate::test::rng(1); |
| let dist = UnitCircle::new(); |
| for _ in 0..1000 { |
| let x = dist.sample(&mut rng); |
| assert_almost_eq!(x[0]*x[0] + x[1]*x[1], 1., 1e-15); |
| } |
| } |
| |
| #[test] |
| fn value_stability() { |
| let mut rng = crate::test::rng(2); |
| let expected = [ |
| [-0.9965658683520504, -0.08280380447614634], |
| [-0.9790853270389644, -0.20345004884984505], |
| [-0.8449189758898707, 0.5348943112253227], |
| ]; |
| let samples = [ |
| UnitCircle.sample(&mut rng), |
| UnitCircle.sample(&mut rng), |
| UnitCircle.sample(&mut rng), |
| ]; |
| assert_eq!(samples, expected); |
| } |
| } |