49 lines
1.4 KiB
Rust
49 lines
1.4 KiB
Rust
// Copyright 2019 Developers of the Rand project.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use num_traits::Float;
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use crate::{uniform::SampleUniform, Distribution, Uniform};
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use rand::Rng;
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/// Samples uniformly from the unit ball (surface and interior) in three
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/// dimensions.
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///
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/// Implemented via rejection sampling.
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///
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///
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/// # Example
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///
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/// ```
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/// use rand_distr::{UnitBall, Distribution};
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///
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/// let v: [f64; 3] = UnitBall.sample(&mut rand::thread_rng());
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/// println!("{:?} is from the unit ball.", v)
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/// ```
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#[derive(Clone, Copy, Debug)]
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#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
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pub struct UnitBall;
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impl<F: Float + SampleUniform> Distribution<[F; 3]> for UnitBall {
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#[inline]
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fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> [F; 3] {
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let uniform = Uniform::new(F::from(-1.).unwrap(), F::from(1.).unwrap());
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let mut x1;
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let mut x2;
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let mut x3;
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loop {
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x1 = uniform.sample(rng);
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x2 = uniform.sample(rng);
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x3 = uniform.sample(rng);
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if x1 * x1 + x2 * x2 + x3 * x3 <= F::from(1.).unwrap() {
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break;
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}
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}
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[x1, x2, x3]
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}
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}
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