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| -rw-r--r-- | src/libstd/rand/mod.rs | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/src/libstd/rand/mod.rs b/src/libstd/rand/mod.rs index c02a97e09a4..b7bf75e39a5 100644 --- a/src/libstd/rand/mod.rs +++ b/src/libstd/rand/mod.rs @@ -70,6 +70,49 @@ //! println!("{}", tuple) //! ``` //! +//! ## Monte Carlo estimation of π +//! +//! For this example, imagine we have a square with sides of length 2 and a unit +//! circle, both centered at the origin. Since the area of a unit circle is π, +//! we have: +//! +//! ```notrust +//! (area of unit circle) / (area of square) = π / 4 +//! ``` +//! +//! So if we sample many points randomly from the square, roughly π / 4 of them +//! should be inside the circle. +//! +//! We can use the above fact to estimate the value of π: pick many points in the +//! square at random, calculate the fraction that fall within the circle, and +//! multiply this fraction by 4. +//! +//! ``` +//! use std::rand; +//! use std::rand::distributions::{IndependentSample, Range}; +//! +//! fn main() { +//! let between = Range::new(-1f64, 1.); +//! let mut rng = rand::task_rng(); +//! +//! let total = 1_000_000u; +//! let mut in_circle = 0u; +//! +//! for _ in range(0u, total) { +//! let a = between.ind_sample(&mut rng); +//! let b = between.ind_sample(&mut rng); +//! if a*a + b*b <= 1. { +//! in_circle += 1; +//! } +//! } +//! +//! // prints something close to 3.14159... +//! println!("{}", 4. * (in_circle as f64) / (total as f64)); +//! } +//! ``` +//! +//! ## Monty Hall Problem +//! //! This is a simulation of the [Monty Hall Problem][]: //! //! > Suppose you're on a game show, and you're given the choice of three doors: |