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Ingy döt Net 2023-07-01 11:58:00 -04:00
parent 7387c8f97b
commit cb5bb5e222
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74
Task/Roots-of-a-quadratic-function/Java/roots-of-a-quadratic-function.java Normal file
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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; // discriminant
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) {
// Avoid calculating -b - Math.sqrt(d), to avoid any
// subtractive cancellation when it is near zero.
double re = (-b + Math.sqrt(d)) / aa;
roots[0] = new Complex(re, 0.0);
roots[1] = new Complex(c / (a * re), 0.0);
} else {
// Avoid calculating -b + Math.sqrt(d).
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}, // two distinct real roots
{6.0, -23.0, 20.0}, // with a != 1.0
{1.0, -1.0e9, 1.0}, // with one root near zero
{1.0, 2.0, 1.0}, // one real root (double root)
{1.0, 0.0, 1.0}, // two imaginary roots
{1.0, 1.0, 1.0} // two complex roots
};
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]);
}
}
}
}