Properly handle flipped limits in trapezoidal_integral (TheAlgorith…

…ms#645)

src/math/trapezoidal_integration.rs

@@ -4,58 +4,39 @@ where
 {
  let delta = (b - a) / precision as f64;
 
- let integral: f64 = (0..precision)
+ (0..precision)
  .map(|trapezoid| {
  let left_side = a + (delta * trapezoid as f64);
  let right_side = left_side + delta;
 
  0.5 * (f(left_side) + f(right_side)) * delta
  })
- .sum();
-
- if a > b {
- -integral
- } else {
- integral
- }
-}
-
-#[allow(dead_code)]
-fn main() {
- let f = |x: f64| x.powi(3);
- let result = trapezoidal_integral(0.0, 1.0, f, 1000);
- println!("{}", result);
+ .sum()
 }
 
 #[cfg(test)]
 mod tests {
  use super::*;
 
- #[test]
- fn test_integral() {
- let f = |x: f64| x.powi(2);
- let result = trapezoidal_integral(0.0, 1.0, f, 1000);
- assert!((result - 1.0 / 3.0).abs() < 0.0001);
- }
-
- #[test]
- fn test_precision() {
- let f = |x: f64| x.powi(2);
- let result = trapezoidal_integral(0.0, 1.0, f, 10000);
- assert!((result - 1.0 / 3.0).abs() < 0.00001);
- }
-
- #[test]
- fn test_negative() {
- let f = |x: f64| x.powi(2);
- let result = trapezoidal_integral(-1.0, 1.0, f, 10000);
- assert!((result - 2.0 / 3.0).abs() < 0.00001);
+ macro_rules! test_trapezoidal_integral {
+ ($($name:ident: $inputs:expr,)*) => {
+ $(
+ #[test]
+ fn $name() {
+ let (a, b, f, prec, expected, eps) = $inputs;
+ let actual = trapezoidal_integral(a, b, f, prec);
+ assert!((actual - expected).abs() < eps);
+ }
+ )*
+ }
  }
 
- #[test]
- fn test_negative_precision() {
- let f = |x: f64| x.powi(2);
- let result = trapezoidal_integral(-1.0, 1.0, f, 100000);
- assert!((result - 2.0 / 3.0).abs() < 0.000001);
+ test_trapezoidal_integral! {
+ basic_0: (0.0, 1.0, |x: f64| x.powi(2), 1000, 1.0/3.0, 0.0001),
+ basic_0_higher_prec: (0.0, 1.0, |x: f64| x.powi(2), 10000, 1.0/3.0, 0.00001),
+ basic_1: (-1.0, 1.0, |x: f64| x.powi(2), 10000, 2.0/3.0, 0.00001),
+ basic_1_higher_prec: (-1.0, 1.0, |x: f64| x.powi(2), 100000, 2.0/3.0, 0.000001),
+ flipped_limits: (1.0, 0.0, |x: f64| x.powi(2), 10000, -1.0/3.0, 0.00001),
+ empty_range: (0.5, 0.5, |x: f64| x.powi(2), 100, 0.0, 0.0000001),
  }
 }