Method eval

tests/root.rs:37–39

(&self, x: [f64; 1])

impl Cubic {
    fn eval(&self, x: [f64; 1]) -> Result<[f64; 1]> {
        Ok([(x[0] - 1f64).powi(3)])
    }
}

impl RootFindingProblem<1, 1, (f64, f64)> for Cubic {