use russell_lab::{vec_approx_eq, StrError, Vector};
use russell_ode::prelude::*;

fn main() -> Result<(), StrError> {
    // ODE system
    let ndim = 1;
    let system = System::new(ndim, |f, x, y, _args: &mut NoArgs| {
        f[0] = x + y[0];
        Ok(())
    });

    // solver
    let params = Params::new(Method::DoPri8);
    let mut solver = OdeSolver::new(params, system)?;

    // initial values
    let x = 0.0;
    let mut y = Vector::from(&[0.0]);

    // solve from x = 0 to x = 1
    let x1 = 1.0;
    let mut args = 0;
    solver.solve(&mut y, x, x1, None, &mut args)?;
    println!("y =\n{}", y);

    // check the results
    let y_ana = Vector::from(&[f64::exp(x1) - x1 - 1.0]);
    vec_approx_eq(&y, &y_ana, 1e-7);

    // print stats
    println!("{}", solver.stats());
    Ok(())
}