rootfinder 0.5.1

/// Perturb a real number.
///
/// # Arguments
///
/// * `x` - Real number, $x\in\mathbb{R}$.
///
/// # Returns
///
/// `x` slightly perturbed.
///
/// # Note
///
/// $x$ is pertubed as $x+100\varepsilon(1+\|x\|)$ where $\varpsilon$ is defined by
/// [`f64::EPSILON`].
pub fn perturb_real(x: f64) -> f64 {
    x + 100.0 * f64::EPSILON * (1.0 + x.abs())
}

#[cfg(test)]
mod tests {
    use super::*;
    use numtest::*;

    #[test]
    fn test_perturb_real_positive() {
        assert_equal!(perturb_real(2.0), 2.0000000000000666);
    }

    #[test]
    fn test_perturb_real_negative() {
        assert_equal!(perturb_real(-2.0), -1.9999999999999334);
    }

    #[test]
    fn test_perturb_real_zero() {
        assert_equal!(perturb_real(0.0), 2.220446049250313e-14);
    }
}