Function delta 

pub fn delta(
    vA: &Vector2<f64>,
    vr: &Vector2<f64>,
    vp: &Vector2<f64>,
) -> Vector2<f64>

The delta function calculates the delta value for the Bairstow’s method

Arguments:

• vA: A vector representing the coefficients of a polynomial equation.
• vr: The parameter vr represents the vector [-2.0, 0.0].
• vp: The parameter vp represents the vector vr - vrj

Returns:

The function delta returns a Vec2 object.

r * p - m -p q * p -m

Examples:

use ginger::rootfinding::delta;
use ginger::vector2::Vector2;

let mut vA1 = Vector2::new(1.0, 2.0);
let vri = Vector2::new(-2.0, 0.0);
let vrj = Vector2::new(4.0, 5.0);
let vd = delta(&vA1, &vri, &vrj);
assert_eq!(vd, Vector2::new(0.2, 0.4));