Examples of lambdas and objects for physics

physics.js

function vdp1(t, y) {
  return [y[1], (1 - y[0] ** 2) * y[1]- y[0]];
}

function van_der_pol(mu) {
  return (t, y) => [y[1], mu * (1 - y[0] ** 2) * y[1] - y[0]];
}

class VdP {
  constructor(mu) {
    this.mu = mu;
  }
  calc(t, y) {
    return [y[1], this.mu * (1 - y[0] ** 2) * y[1] - y[0]];
  }
}

const ovdp1 = new VdP(1);

console.log('vdp a:', vdp1(0, [2, 0]));
console.log('vdp b:', van_der_pol(1)(0, [2, 0]));
console.log('vdp c:', ovdp1.calc(0, [2, 0]));

function pendulum(t, theta) {
  g = 9.81;
  l = 1;
  return [-g/l * Math.sin(theta[1]), theta[0]];;
}

function gen_pendulum(g, l) {
  return (t, theta) => [-g/l * Math.sin(theta[1]), theta[0]];
}

class Pendulum {
  constructor(g, l) {
    this.g = g;
    this.l = l;
  }
  calc(t, theta) {
    return [-this.g/this.l * Math.sin(theta[1]), theta[0]];
  }
}

const opendulum = new Pendulum(9.81, 1);

console.log('pendulum a:', pendulum(0, [0, Math.PI / 4]));
console.log('pendulum b:', gen_pendulum(9.81, 1)(0, [0, Math.PI / 4]));
console.log('pendulum c:', opendulum.calc(0, [0, Math.PI / 4]));