fix: rk23 coefficient

Cargo.toml

@@ -11,10 +11,6 @@ readme = "README.md"
 keywords =["numeric", "science", "integration", "quadrature"]
 categories =["science"]
 
-[dev-dependencies]
-float-cmp = "0.9"
-rand = "0.8"
-
 [dependencies]
 nalgebra = "0.32"
 num-complex = "0.4"
@@ -25,3 +21,8 @@ typenum = "1.17"
 
 [build-dependencies]
 phf_codegen = "0.11"
+
+[dev-dependencies]
+float-cmp = "0.9"
+rand = "0.8"
+rstest = "0.26.1"

src/ivp/rk.rs

@@ -615,14 +615,14 @@ impl<N: ComplexField> RungeKuttaCoefficients<4> for RK23Coefficients<N> {
             -Self::RealField::from_u8(5)? / Self::RealField::from_u8(72)?,
             Self::RealField::from_u8(12)?.recip(),
             Self::RealField::from_u8(9)?.recip(),
-            Self::RealField::from_u8(8)?.recip(),
+            -Self::RealField::from_u8(8)?.recip(),
         ]))
     }
 }
 
 /// Bogacki-Shampine method for solving an IVP.
 ///
-/// Defines the Butcher Tableaux for a 5(4) order adaptive
+/// Defines the Butcher Tableaux for a 3(2) order adaptive
 /// Runge-Kutta method. Uses [`RungeKutta`] to do the actual solving.
 /// Provides an implementation of the [`IVPSolver`] trait.
 ///
@@ -659,6 +659,7 @@ pub type RungeKutta23<'a, N, D, T, F> = RungeKutta<'a, N, D, 4, T, F, RK23Coeffi
 mod test {
     use super::*;
     use crate::{ivp::UserError, BSVector};
+    use rstest::rstest;
 
     fn quadratic_deriv(t: f64, _y: &[f64], _: &mut ()) -> Result<BSVector<f64, 1>, UserError> {
         Ok(BSVector::from_column_slice(&[-2.0 * t]))
@@ -668,13 +669,27 @@ mod test {
         Ok(BSVector::from_column_slice(&[t.cos()]))
     }
 
-    #[test]
-    fn rungekutta45_quadratic() {
+    type TestRK<'a, const O: usize, R> = RungeKutta<
+        'a,
+        f64,
+        Const<1>,
+        O,
+        (),
+        fn(f64, &[f64], &mut ()) -> Result<BVector<f64, Const<1>>, UserError>,
+        R,
+    >;
+
+    #[rstest]
+    #[case::rk23(RungeKutta23::new().unwrap())]
+    #[case::rk45(RungeKutta45::new().unwrap())]
+    fn rungekutta_quadratic<'a, const O: usize, R>(#[case] rk: TestRK<'a, O, R>)
+    where
+        R: RungeKuttaCoefficients<O, RealField = f64>,
+    {
         let t_initial = 0.0;
         let t_final = 10.0;
 
-        let solver = RungeKutta45::new()
-            .unwrap()
+        let solver = rk
             .with_minimum_dt(0.0001)
             .unwrap()
             .with_maximum_dt(0.1)
@@ -703,13 +718,17 @@ mod test {
         }
     }
 
-    #[test]
-    fn rungekutta45_sine() {
+    #[rstest]
+    #[case::rk23(RungeKutta23::new().unwrap())]
+    #[case::rk45(RungeKutta45::new().unwrap())]
+    fn rungekutta_sine<'a, const O: usize, R>(#[case] rk: TestRK<'a, O, R>)
+    where
+        R: RungeKuttaCoefficients<O, RealField = f64>,
+    {
         let t_initial = 0.0;
         let t_final = 10.0;
 
-        let solver = RungeKutta45::new()
-            .unwrap()
+        let solver = rk
             .with_minimum_dt(0.001)
             .unwrap()
             .with_maximum_dt(0.01)