Sundials is a s̲u̲ite of n̲onlinear and d̲i̲fferential/a̲l̲gebraic equation s̲olvers.
The following code solves the equation ∂ₜu = f(t,u) where f is the function (t,u) ↦ 1 using Adams' method.
use sundials::{context, cvode::CVode};
fn main() -> Result<(), Box<sundials::Error>> {
let mut ode = CVode::adams(0., &[0.], |t, u, du| *du = [1.])
.build(context!()?)?;
let mut u1 = [f64::NAN];
ode.solve(2., &mut u1);
assert_eq!(u1, [2.]);
let (u2, _) = ode.cauchy(0., &[0.], 1.);
assert_eq!(u2[0], 1.);
Ok(())
}Then u[0] contains the solution u at time t=1 and u[1] the
speed ∂ₜu(1).