INNER CODE UNIT · TypeScript
D
margelo/react-native-graph · src/GetYForX.ts:60
const D = (q * q) / 4 + (p * p * p) / 27;
if (Math.abs(D) < 1e-8) {
// D = 0 -> two roots
roots = [(-1.5 * q) / p, (3 * q) / p];
} else if (D > 0) {
// Only one real root
const u = cuberoot(-q / 2 - Math.sqrt(D));
roots = [u - p / (3 * u)];
} else {
// D < 0, three roots, but needs to use complex numbers/trigonometric solution
const u = 2 * Math.sqrt(-p / 3);
const t = Math.acos((3 * q) / p / u) / 3; // D < 0 implies p < 0 and acos argument in [-1..1]
const k = (2 * Math.PI) / 3;
roots = [u * Math.cos(t), u * Math.cos(t - k), u * Math.cos(t - 2 * k)];
}
}
// Convert back from depressed cubic