Task: Roots of a quadratic function




Go: package main

import (
    "fmt"
    "math"
)

func qr(a, b, c float64) ([]float64, []complex128) {
    d := b*b-4*a*c
    switch {
    case d == 0:
        
        return []float64{-b/(2*a)}, nil
    case d > 0:
        
        if b < 0 {
            d = math.Sqrt(d)-b
        } else {
            d = -math.Sqrt(d)-b
        }
        return []float64{d/(2*a), (2*c)/d}, nil
    case d < 0:
        

        den := 1/(2*a)
        t1 := complex(-b*den, 0)
        t2 := complex(0, math.Sqrt(-d)*den)
        return nil, []complex128{t1+t2, t1-t2}
    }
    
    return []float64{d}, nil
}

func test(a, b, c float64) {
    fmt.Print("coefficients: ", a, b, c, " -> ")
    r, i := qr(a, b, c)
    switch len(r) {
    case 1:
        fmt.Println("one real root:", r[0])
    case 2:
        fmt.Println("two real roots:", r[0], r[1])
    default:
        fmt.Println("two complex roots:", i[0], i[1])
    }
}

func main() {
    for _, c := range [][3]float64{
        {1, -2, 1},
        {1, 0, 1},
        {1, -10, 1},
        {1, -1000, 1},
        {1, -1e9, 1},
    } {
        test(c[0], c[1], c[2])
    }
}


Java: public class QuadraticRoots {
    private static class Complex {
        double re, im;

        public Complex(double re, double im) {
            this.re = re;
            this.im = im;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj == this) {return true;}
            if (!(obj instanceof Complex)) {return false;}
            Complex other = (Complex) obj;
            return (re == other.re) && (im == other.im);
        }

        @Override
        public String toString() {
            if (im == 0.0) {return String.format("%g", re);}
            if (re == 0.0) {return String.format("%gi", im);}
            return String.format("%g %c %gi", re,
                (im < 0.0 ? '-' : '+'), Math.abs(im));
        }
    }

    private static Complex[] quadraticRoots(double a, double b, double c) {
        Complex[] roots = new Complex[2];
        double d = b * b - 4.0 * a * c;  
        double aa = a + a;

        if (d < 0.0) {
            double re = -b / aa;
            double im = Math.sqrt(-d) / aa;
            roots[0] = new Complex(re, im);
            roots[1] = new Complex(re, -im);
        } else if (b < 0.0) {
            
            
            double re = (-b + Math.sqrt(d)) / aa;
            roots[0] = new Complex(re, 0.0);
            roots[1] = new Complex(c / (a * re), 0.0);
        } else {
            
            double re = (-b - Math.sqrt(d)) / aa;
            roots[1] = new Complex(re, 0.0);
            roots[0] = new Complex(c / (a * re), 0.0);
        }
        return roots;
    }

    public static void main(String[] args) {
        double[][] equations = {
            {1.0, 22.0, -1323.0},   
            {6.0, -23.0, 20.0},     
            {1.0, -1.0e9, 1.0},     
            {1.0, 2.0, 1.0},        
            {1.0, 0.0, 1.0},        
            {1.0, 1.0, 1.0}         
        };
        for (int i = 0; i < equations.length; i++) {
            Complex[] roots = quadraticRoots(
                equations[i][0], equations[i][1], equations[i][2]);
            System.out.format("%na = %g   b = %g   c = %g%n",
                equations[i][0], equations[i][1], equations[i][2]);
            if (roots[0].equals(roots[1])) {
                System.out.format("X1,2 = %s%n", roots[0]);
            } else {
                System.out.format("X1 = %s%n", roots[0]);
                System.out.format("X2 = %s%n", roots[1]);
            }
        }
    }
}