Dependency updates

Cargo.toml

@@ -1,15 +1,29 @@
 [package]
-name = "differential_equations"
-version = "0.2.1"
+name = "ordinary-diffeq"
+version = "0.2.3"
 edition = "2021"
+authors = ["Connor Johnstone"]
+description = "A library for solving differential equations based on the DifferentialEquations.jl julia library."
+readme = "readme.md"
+repository = "https://gitlab.rcjohnstone.com/connor/differential-equations"
+license = "MIT"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
-nalgebra = { version = "0.32", features = ["serde-serialize"] }
-num-traits = "0.2.15"
+nalgebra = { version = "0.34", features = ["serde-serialize"] }
+num-traits = "0.2.19"
 roots = "0.0.8"
 
 [dev-dependencies]
 approx = "0.5"
+criterion = "0.7.0"
+
+[[bench]]
+name = "simple_1d"
+harness = false
+
+[[bench]]
+name = "orbit"
+harness = false

benches/orbit.rs

@@ -0,0 +1,40 @@
+use criterion::{criterion_group, criterion_main, Criterion};
+
+use ordinary_diffeq::prelude::*;
+use nalgebra::Vector6;
+
+fn bench_orbit(c: &mut Criterion) {
+    let mu = 3.98600441500000e14;
+
+    // Set up the system
+    type Params = (f64,);
+    let params = (mu,);
+    fn derivative(_t: f64, state: Vector6<f64>, p: &Params) -> Vector6<f64> {
+        let acc = -(p.0 * state.fixed_rows::<3>(0)) / (state.fixed_rows::<3>(0).norm().powi(3));
+        Vector6::new(state[3], state[4], state[5], acc[0], acc[1], acc[2])
+    }
+    let y0 = Vector6::new(
+        4.263868426884883e6,
+        5.146189057155391e6,
+        1.1310208421331816e6,
+        -5923.454461876975,
+        4496.802639690076,
+        1870.3893008991558,
+    );
+
+    // Integrate
+    let ode = ODE::new(&derivative, 0.0, 86400.0, y0, params);
+    let dp45 = DormandPrince45::new();
+    let controller = PIController::new(0.37, 0.04, 10.0, 0.2, 1000.0, 0.9, 0.01);
+
+    c.bench_function("bench_orbit", |b| {
+        b.iter(|| {
+            std::hint::black_box({
+                Problem::new(ode, dp45, controller).solve();
+            });
+        });
+    });
+}
+
+criterion_group!(benches, bench_orbit);
+criterion_main!(benches);

benches/simple_1d.rs

@@ -0,0 +1,56 @@
+use criterion::{criterion_group, criterion_main, Criterion};
+
+use ordinary_diffeq::prelude::*;
+use nalgebra::Vector1;
+
+fn bench_simple_1d(c: &mut Criterion) {
+    type Params = (f64,);
+    let params = (0.1,);
+
+    fn derivative(_t: f64, y: Vector1<f64>, p: &Params) -> Vector1<f64> {
+        Vector1::new(-p.0 * y[0])
+    }
+
+    let y0 = Vector1::new(1.0);
+
+    // Set up the problem (ODE, Integrator, Controller, and Callbacks)
+    let ode = ODE::new(&derivative, 0.0, 10.0, y0, params);
+    let dp45 = DormandPrince45::new().a_tol(1e-6).r_tol(1e-6);
+    let controller = PIController::default();
+
+    c.bench_function("bench_simple_1d", |b| {
+        b.iter(|| {
+            std::hint::black_box({
+                Problem::new(ode, dp45, controller).solve();
+            });
+        });
+    });
+}
+
+fn bench_interpolation_1d(c: &mut Criterion) {
+    type Params = (f64,);
+    let params = (0.1,);
+
+    fn derivative(_t: f64, y: Vector1<f64>, p: &Params) -> Vector1<f64> {
+        Vector1::new(-p.0 * y[0])
+    }
+
+    let y0 = Vector1::new(1.0);
+
+    // Set up the problem (ODE, Integrator, Controller, and Callbacks)
+    let ode = ODE::new(&derivative, 0.0, 10.0, y0, params);
+    let dp45 = DormandPrince45::new().a_tol(1e-6).r_tol(1e-6);
+    let controller = PIController::default();
+
+    c.bench_function("bench_interpolation_1d", |b| {
+        b.iter(|| {
+            std::hint::black_box({
+                let solution = Problem::new(ode, dp45, controller).solve();
+                let _ = (0..100).map(|t| solution.interpolate(t as f64 * 0.1)[0]);
+            });
+        });
+    });
+}
+
+criterion_group!(benches, bench_simple_1d, bench_interpolation_1d,);
+criterion_main!(benches);

readme.md

@@ -53,7 +53,7 @@ let y0 = Vector2::new(0.0, PI/2.0);
 
 // Set up the problem (ODE, Integrator, Controller, and Callbacks)
 let ode = ODE::new(&derivative, 0.0, 6.3, y0, params);
-let dp45 = DormandPrince45::new(1e-12_f64, 1e-6_f64);
+let dp45 = DormandPrince45::new().a_tol(1e-12).r_tol(1e-6);
 let controller = PIController::default();
 
 let value_too_high = Callback {

src/callback.rs

@@ -11,11 +11,11 @@ pub struct Callback<'a, const D: usize, P> {
     pub event: &'a dyn Fn(f64, SVector<f64, D>, &P) -> f64,
 
     /// The function to change the ODE
-    pub effect: &'a dyn Fn(&mut ODE<D, P>) -> (),
+    pub effect: &'a dyn Fn(&mut ODE<D, P>),
 }
 
 /// A convenience function for stopping the integration
-pub fn stop<'a, const D: usize, P>(ode: &mut ODE<D, P>) -> () {
+pub fn stop<const D: usize, P>(ode: &mut ODE<D, P>) {
     ode.t_end = ode.t;
 }
 

src/controller.rs

@@ -1,5 +1,31 @@
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum TryStep {
+    Accepted(f64, f64),
+    NotYetAccepted(f64),
+}
+
+impl TryStep {
+    pub fn extract(&self) -> f64 {
+        match self {
+            TryStep::Accepted(h, _) => *h,
+            TryStep::NotYetAccepted(h) => *h,
+        }
+    }
+
+    pub fn is_accepted(&self) -> bool {
+        matches!(self, TryStep::Accepted(_, _))
+    }
+
+    pub fn reset(&mut self) -> Result<TryStep, &str> {
+        match self {
+            TryStep::Accepted(_, h) => Ok(TryStep::NotYetAccepted(*h)),
+            TryStep::NotYetAccepted(_) => Err("Cannot reset a NotYetAccepted TryStep"),
+        }
+    }
+}
+
 pub trait Controller<const D: usize> {
-    fn determine_step(&mut self, h: f64, err: f64) -> (bool, f64);
+    fn determine_step(&mut self, h: f64, err: f64) -> TryStep;
 }
 
 #[derive(Debug, Clone, Copy)]
@@ -11,32 +37,30 @@ pub struct PIController {
     pub factor_old: f64,
     pub h_max: f64,
     pub safety_factor: f64,
-    pub old_h: f64,
+    pub next_step_guess: TryStep,
 }
 
 impl<const D: usize> Controller<D> for PIController {
     /// Determines if the previously run step size and error were valid or not. Either way, it also
     /// returns what the next step size should be
-    fn determine_step(&mut self, h: f64, err: f64) -> (bool, f64) {
+    fn determine_step(&mut self, prev_step: f64, err: f64) -> TryStep {
         let factor_11 = err.powf(self.alpha);
         let factor = self.factor_c2.max(
             self.factor_c1
                 .min(factor_11 * self.factor_old.powf(-self.beta) / self.safety_factor),
         );
-        let mut h_new = h / factor;
         if err <= 1.0 {
-            // Accept the stepsize
+            let mut h = prev_step / factor;
+            // Accept the stepsize and provide what the next step size should be
             self.factor_old = err.max(1.0e-4);
-            if h_new.abs() > self.h_max {
-                // If the step is too big
-                h_new = self.h_max.copysign(h_new);
+            if h.abs() > self.h_max {
+                // If the step goes past the maximum allowed, though, we shrink it
+                h = self.h_max.copysign(h);
             }
-            (true, h_new)
-            // (true, h_new)
+            TryStep::Accepted(prev_step, h)
         } else {
-            // Reject the stepsize and propose a smaller one
-            h_new = h / (self.factor_c1.min(factor_11 / self.safety_factor));
-            (false, h_new)
+            // Reject the stepsize and propose a smaller one for the current step
+            TryStep::NotYetAccepted(prev_step / (self.factor_c1.min(factor_11 / self.safety_factor)))
         }
     }
 }
@@ -52,17 +76,20 @@ impl PIController {
         initial_h: f64,
     ) -> Self {
         Self {
-            alpha: alpha,
-            beta: beta,
+            alpha,
+            beta,
             factor_c1: 1.0 / min_factor,
             factor_c2: 1.0 / max_factor,
             factor_old: 1.0e-4,
             h_max: h_max.abs(),
-            safety_factor: safety_factor,
-            old_h: initial_h,
+            safety_factor,
+            next_step_guess: TryStep::NotYetAccepted(initial_h),
         }
     }
-    pub fn default() -> Self {
+}
+
+impl Default for PIController {
+    fn default() -> Self {
         Self::new(0.17, 0.04, 10.0, 0.2, 100000.0, 0.9, 1e-4)
     }
 }
@@ -82,6 +109,6 @@ mod tests {
         assert!(controller.factor_old == 1.0e-4);
         assert!(controller.h_max == 10.0);
         assert!(controller.safety_factor == 0.9);
-        assert!(controller.old_h == 1e-4);
+        assert!(controller.next_step_guess == TryStep::NotYetAccepted(1e-4));
     }
 }

src/integrator/dormand_prince.rs

@@ -13,7 +13,7 @@ pub trait DormandPrinceIntegrator<'a> {
 
 #[derive(Debug, Clone, Copy)]
 pub struct DormandPrince45<const D: usize> {
-    a_tol: f64,
+    a_tol: SVector<f64,D>,
     r_tol: f64,
 }
 
@@ -21,8 +21,17 @@ impl<const D: usize> DormandPrince45<D>
 where
     DormandPrince45<D>: Integrator<D>,
 {
-    pub fn new(a_tol: f64, r_tol: f64) -> Self {
-        Self { a_tol, r_tol }
+    pub fn new() -> Self {
+        Self { a_tol: SVector::<f64,D>::from_element(1e-8), r_tol: 1e-8 }
+    }
+    pub fn a_tol(&mut self, a_tol: f64) -> Self {
+        Self { a_tol: SVector::<f64,D>::from_element(a_tol), r_tol: self.r_tol }
+    }
+    pub fn a_tol_full(&mut self, a_tol: SVector::<f64,D>) -> Self {
+        Self { a_tol, r_tol: self.r_tol }
+    }
+    pub fn r_tol(&mut self, r_tol: f64) -> Self {
+        Self { a_tol: self.a_tol, r_tol }
     }
 }
 
@@ -93,7 +102,7 @@ where
         h: f64,
     ) -> (SVector<f64, D>, Option<f64>, Option<Vec<SVector<f64, D>>>) {
         let mut k: Vec<SVector<f64, D>> = vec![SVector::<f64, D>::zeros(); Self::STAGES];
-        let mut next_y = ode.y.clone();
+        let mut next_y = ode.y;
         let mut err = SVector::<f64, D>::zeros();
         let mut rcont5 = SVector::<f64, D>::zeros();
         // Do the first of the summations
@@ -106,8 +115,8 @@ where
         for i in 1..Self::STAGES {
             // Compute the ks
             let mut y_term = SVector::<f64, D>::zeros();
-            for j in 0..i {
-                y_term += k[j] * Self::A[(i * (i - 1)) / 2 + j];
+            for (j, item) in k.iter().enumerate().take(i) {
+                y_term += item * Self::A[(i * (i - 1)) / 2 + j];
             }
             k[i] = (ode.f)(ode.t + Self::C[i] * h, ode.y + y_term * h, &ode.params);
 
@@ -119,7 +128,7 @@ where
         let rcont2 = next_y - ode.y;
         let rcont3 = h * k[0] - rcont2;
         let rcont4 = rcont2 - k[Self::STAGES - 1] * h - rcont3;
-        let tol = SVector::<f64, D>::repeat(self.a_tol) + ode.y * self.r_tol;
+        let tol = self.a_tol + ode.y * self.r_tol;
         let rcont = vec![rcont1, rcont2, rcont3, rcont4, rcont5];
         (next_y, Some((err.component_div(&tol)).norm()), Some(rcont))
     }
@@ -127,7 +136,7 @@ where
         &self,
         t_start: f64,
         t_end: f64,
-        dense: &Vec<SVector<f64, D>>,
+        dense: &[SVector<f64, D>],
         t: f64,
     ) -> SVector<f64, D> {
         let s = (t - t_start) / (t_end - t_start);

src/integrator/mod.rs

@@ -22,7 +22,7 @@ pub trait Integrator<const D: usize> {
         &self,
         t_start: f64,
         t_end: f64,
-        dense: &Vec<SVector<f64, D>>,
+        dense: &[SVector<f64, D>],
         t: f64,
     ) -> SVector<f64, D>;
 }
@@ -44,7 +44,7 @@ mod tests {
         let y0 = Vector3::new(1.0, 1.0, 1.0);
         let mut ode = ODE::new(&derivative, 0.0, 4.0, y0, ());
 
-        let dp45 = DormandPrince45::new(1e-12_f64, 1e-4_f64);
+        let dp45 = DormandPrince45::new().a_tol(1e-12).r_tol(1e-4);
 
         // Test that y'(t) = y(t) solves to y(t) = e^t for rkf54
         // and also that the error seems reasonable

src/lib.rs

@@ -18,7 +18,7 @@ pub mod prelude {
 mod tests {
     use crate::prelude::*;
     use approx::assert_relative_eq;
-    use nalgebra::{Vector2, Vector6};
+    use nalgebra::{Vector1, Vector2, Vector6};
     use std::f64::consts::PI;
 
     #[test]
@@ -38,7 +38,7 @@ mod tests {
 
         // Set up the problem (ODE, Integrator, Controller, and Callbacks)
         let ode = ODE::new(&derivative, 0.0, 6.3, y0, params);
-        let dp45 = DormandPrince45::new(1e-12_f64, 1e-6_f64);
+        let dp45 = DormandPrince45::new().a_tol(1e-12).r_tol(1e-6);
         let controller = PIController::default();
 
         let value_too_high = Callback {
@@ -54,6 +54,32 @@ mod tests {
         let _interpolated_answer = solution.interpolate(4.4);
     }
 
+    #[test]
+    fn test_correctness() {
+        // Define the system (parameters, derivative, and initial state)
+        type Params = ();
+        let params = ();
+
+        fn derivative(_t: f64, y: Vector1<f64>, _p: &Params) -> Vector1<f64> {
+            Vector1::new(5.0 * y[0] - 3.0)
+        }
+
+        let y0 = Vector1::new(1.0);
+
+        // Set up the problem (ODE, Integrator, Controller, and Callbacks)
+        let ode = ODE::new(&derivative, 2.0, 3.0, y0, params);
+        let dp45 = DormandPrince45::new();
+        let controller = PIController::default();
+
+        // Solve the problem
+        let mut problem = Problem::new(ode, dp45, controller);
+        let solution = problem.solve();
+        for (time, state) in solution.times.iter().zip(solution.states.iter()) {
+            let exact = 0.4 * (5.0 * (time - 2.0)).exp() + 0.6;
+            assert_relative_eq!(state[0], exact, max_relative = 1e-7);
+        }
+    }
+
     #[test]
     fn test_orbit() {
         // Calculate one period
@@ -79,11 +105,9 @@ mod tests {
 
         // Integrate
         let ode = ODE::new(&derivative, 0.0, 10.0 * period, y0, params);
-        let dp45 = DormandPrince45::new(1e-12_f64, 1e-12_f64);
+        let dp45 = DormandPrince45::new().a_tol(1e-12).r_tol(1e-12);
         let controller = PIController::new(0.37, 0.04, 10.0, 0.2, 1000.0, 0.9, 0.01);
-
         let mut problem = Problem::new(ode, dp45, controller);
-
         let solution = problem.solve();
 
         assert_relative_eq!(

src/ode.rs

@@ -1,10 +1,12 @@
 use nalgebra::SVector;
 
+type ProblemFunction<'a, const D: usize, P> = &'a dyn Fn(f64, SVector<f64, D>, &P) -> SVector<f64, D>;
+
 /// The basic ODE object that will be passed around. The type (T) and the size (D) will be
 /// determined upon creation of the object
 #[derive(Clone, Copy)]
 pub struct ODE<'a, const D: usize, P> {
-    pub f: &'a dyn Fn(f64, SVector<f64, D>, &P) -> SVector<f64, D>,
+    pub f: ProblemFunction<'a, D, P>,
     pub y: SVector<f64, D>,
     pub t: f64,
     pub params: P,
@@ -16,7 +18,7 @@ pub struct ODE<'a, const D: usize, P> {
 
 impl<'a, const D: usize, P> ODE<'a, D, P> {
     pub fn new(
-        f: &'a (dyn Fn(f64, SVector<f64, D>, &P) -> SVector<f64, D>),
+        f: ProblemFunction<'a, D, P>,
         t0: f64,
         t_end: f64,
         y0: SVector<f64, D>,

src/problem.rs

@@ -1,8 +1,8 @@
 use nalgebra::SVector;
-use roots::{find_root_brent, DebugConvergency};
+use roots::{find_root_brent, SimpleConvergency};
 
 use super::callback::Callback;
-use super::controller::{Controller, PIController};
+use super::controller::{Controller, PIController, TryStep};
 use super::integrator::Integrator;
 use super::ode::ODE;
 
@@ -23,48 +23,64 @@ where
 {
     pub fn new(ode: ODE<'a, D, P>, integrator: S, controller: PIController) -> Self {
         Problem {
-            ode: ode,
-            integrator: integrator,
-            controller: controller,
+            ode,
+            integrator,
+            controller,
             callbacks: Vec::new(),
         }
     }
     pub fn solve(&mut self) -> Solution<S, D> {
-        let mut convergency = DebugConvergency::new(1e-12, 50);
+        let mut convergency = SimpleConvergency {
+            eps: 1e-12,
+            max_iter: 1000,
+        };
         let mut times: Vec<f64> = vec![self.ode.t];
         let mut states: Vec<SVector<f64, D>> = vec![self.ode.y];
         let mut dense_coefficients: Vec<Vec<SVector<f64, D>>> = Vec::new();
-        let mut step: f64 = self.controller.old_h;
-        let (mut new_y, mut err_option, _) = self.integrator.step(&self.ode, 0.0);
         while self.ode.t < self.ode.t_end {
-            let mut dense_option: Option<Vec<SVector<f64, D>>> = None;
-            if S::ADAPTIVE {
+            if self.ode.t + self.controller.next_step_guess.extract() > self.ode.t_end {
+                // If the next step would go past the end, then just set it to the end
+                self.controller.next_step_guess = TryStep::NotYetAccepted(
+                    self.ode.t_end - self.ode.t,
+                );
+            }
+            let (mut new_y, mut curr_step, mut dense_option) = if S::ADAPTIVE {
+                // First, we try stepping with the "next step guess" to get the error
+                let (mut trial_y, mut err_option, mut dense_option) =
+                    self.integrator.step(&self.ode, self.controller.next_step_guess.extract());
                 let mut err = err_option.unwrap();
-                let mut accepted: bool = false;
-                while !accepted {
-                    // Try a step and if that isn't acceptable, then change the step until it is
-                    (accepted, step) = <PIController as Controller<D>>::determine_step(
+                // Then we determine whether we need to reduce the step size or not
+                // If successful, we get the next step guess
+                let initial_guess = self.controller.next_step_guess.extract();
+                let mut next_step_guess = <PIController as Controller<D>>::determine_step(
                     &mut self.controller,
-                        step,
+                    initial_guess,
+                    err,
+                );
+                while !next_step_guess.is_accepted() {
+                    // If that step isn't acceptable, then change the step until it is
+                    (trial_y, err_option, dense_option) =
+                        self.integrator.step(&self.ode, next_step_guess.extract());
+                    next_step_guess = <PIController as Controller<D>>::determine_step(
+                        &mut self.controller,
+                        next_step_guess.extract(),
                         err,
                     );
-                    (new_y, err_option, dense_option) = self.integrator.step(&self.ode, step);
                     err = err_option.unwrap();
                 }
-                self.controller.old_h = step;
-                self.controller.h_max = self
-                    .controller
-                    .h_max
-                    .min(self.ode.t_end - self.ode.t - step);
+                // So at this point we can safely assume we have an accepted step
+                self.controller.next_step_guess = next_step_guess.reset().unwrap();
+                (trial_y, next_step_guess.extract(), dense_option)
             } else {
                 // If fixed time step just step forward one step
-                (new_y, _, dense_option) = self.integrator.step(&self.ode, step);
-            }
-            if self.callbacks.len() > 0 {
+                let (trial_y, _, dense_option) = self.integrator.step(&self.ode, self.controller.next_step_guess.extract());
+                (trial_y, self.controller.next_step_guess.extract(), dense_option)
+            };
+            if !self.callbacks.is_empty() {
                 // Check for events occurring
                 for callback in &self.callbacks {
                     if (callback.event)(self.ode.t, self.ode.y, &self.ode.params)
-                        * (callback.event)(self.ode.t + step, new_y, &self.ode.params)
+                        * (callback.event)(self.ode.t + curr_step, new_y, &self.ode.params)
                         < 0.0
                     {
                         // If the event crossed zero, then find the root
@@ -72,15 +88,15 @@ where
                             let test_y = self.integrator.step(&self.ode, test_t).0;
                             (callback.event)(self.ode.t + test_t, test_y, &self.ode.params)
                         };
-                        let root = find_root_brent(0.0, step, &f, &mut convergency).unwrap();
-                        step = root;
-                        (new_y, _, dense_option) = self.integrator.step(&self.ode, step);
+                        let root = find_root_brent(0.0, curr_step, &f, &mut convergency).unwrap();
+                        curr_step = root;
+                        (new_y, _, dense_option) = self.integrator.step(&self.ode, curr_step);
                         (callback.effect)(&mut self.ode);
                     }
                 }
             }
             self.ode.y = new_y;
-            self.ode.t += step;
+            self.ode.t += curr_step;
             times.push(self.ode.t);
             states.push(self.ode.y);
             // TODO: Implement third order interpolation for non-dense algorithms
@@ -134,14 +150,9 @@ where
         }
 
         // Then find the two t values closest to the desired t
-        let mut end_index: usize = 0;
-        for (i, time) in self.times.iter().enumerate() {
-            if time > &t {
-                end_index = i;
-                break;
-            }
-        }
-
+        match times.binary_search_by(|x| x.total_cmp(&t)) {
+            Ok(index) => self.states[index],
+            Err(end_index) => {
                 // Then send that to the integrator
                 let t_start = times[end_index - 1];
                 let t_end = times[end_index];
@@ -149,6 +160,8 @@ where
                     .interpolate(t_start, t_end, &self.dense[end_index - 1], t)
             }
         }
+    }
+}
 
 #[cfg(test)]
 mod tests {
@@ -168,7 +181,7 @@ mod tests {
         let y0 = Vector3::new(1.0, 1.0, 1.0);
 
         let ode = ODE::new(&derivative, 0.0, 1.0, y0, ());
-        let dp45 = DormandPrince45::new(1e-12_f64, 1e-5_f64);
+        let dp45 = DormandPrince45::new().a_tol(1e-12).r_tol(1e-5);
         let controller = PIController::default();
 
         let mut problem = Problem::new(ode, dp45, controller);
@@ -192,7 +205,7 @@ mod tests {
         let y0 = Vector3::new(1.0, 1.0, 1.0);
 
         let ode = ODE::new(&derivative, 0.0, 10.0, y0, ());
-        let dp45 = DormandPrince45::new(1e-12_f64, 1e-5_f64);
+        let dp45 = DormandPrince45::new().a_tol(1e-12).r_tol(1e-5);
         let controller = PIController::default();
 
         let value_too_high = Callback {
@@ -203,7 +216,11 @@ mod tests {
         let mut problem = Problem::new(ode, dp45, controller).with_callback(value_too_high);
         let solution = problem.solve();
 
-        assert!(solution.states.last().unwrap()[0] == 10.0);
+        assert_relative_eq!(
+            solution.states.last().unwrap()[0],
+            10.0,
+            max_relative = 1e-11
+        );
     }
 
     #[test]
@@ -215,7 +232,7 @@ mod tests {
         let y0 = Vector3::new(1.0, 1.0, 1.0);
 
         let ode = ODE::new(&derivative, 0.0, 10.0, y0, ());
-        let dp45 = DormandPrince45::new(1e-12_f64, 1e-6_f64);
+        let dp45 = DormandPrince45::new().a_tol(1e-12).r_tol(1e-6);
         let controller = PIController::default();
 
         let mut problem = Problem::new(ode, dp45, controller);