72 lines
1.8 KiB
Rust
72 lines
1.8 KiB
Rust
// Copyright 2018 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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//! The Weibull distribution.
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use Rng;
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use distributions::{Distribution, OpenClosed01};
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/// Samples floating-point numbers according to the Weibull distribution
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///
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/// # Example
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/// ```
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/// use rand::prelude::*;
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/// use rand::distributions::Weibull;
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///
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/// let val: f64 = SmallRng::from_entropy().sample(Weibull::new(1., 10.));
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/// println!("{}", val);
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/// ```
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#[derive(Clone, Copy, Debug)]
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pub struct Weibull {
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inv_shape: f64,
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scale: f64,
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}
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impl Weibull {
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/// Construct a new `Weibull` distribution with given `scale` and `shape`.
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///
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/// # Panics
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///
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/// `scale` and `shape` have to be non-zero and positive.
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pub fn new(scale: f64, shape: f64) -> Weibull {
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assert!((scale > 0.) & (shape > 0.));
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Weibull { inv_shape: 1./shape, scale }
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}
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}
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impl Distribution<f64> for Weibull {
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fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> f64 {
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let x: f64 = rng.sample(OpenClosed01);
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self.scale * (-x.ln()).powf(self.inv_shape)
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}
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}
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#[cfg(test)]
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mod tests {
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use distributions::Distribution;
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use super::Weibull;
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#[test]
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#[should_panic]
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fn invalid() {
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Weibull::new(0., 0.);
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}
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#[test]
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fn sample() {
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let scale = 1.0;
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let shape = 2.0;
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let d = Weibull::new(scale, shape);
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let mut rng = ::test::rng(1);
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for _ in 0..1000 {
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let r = d.sample(&mut rng);
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assert!(r >= 0.);
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}
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}
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}
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