Stellar magnetic field

vectorfield.js

const sub = (a, b) => [
  a[0] - b[0],
  a[1] - b[1],
];

const distance = (a, b) => Math.sqrt(
  Math.pow(a[0] - b[0], 2) + 
  Math.pow(a[1] - b[1], 2)
);

const length = (a) => Math.sqrt(
  Math.pow(a[0], 2) + 
  Math.pow(a[1], 2)
);

const normalize = (a) => {
  const l = length(a);
  return [
    a[0] / l,
    a[1] / l,
  ];
};

const rand = (n) => {
  const f = Math.sin(n) * 4375.5453123;
  return f - Math.floor(f);
};

// What function to produce streamlines for
let vectorField = function(p) {
  p = [p.x, p.y];
  let v = [0,0];
  let o, r, s, m, d;
  const limit = 12.;
  for (let i = 0; i < limit; i++) {
    r = rand(i/limit) - .5;
    o = i + r * 2.;
    a = [
      Math.sin(o / limit * Math.PI * 2),
      Math.cos(o / limit * Math.PI * 2)
    ];
    a[0] *= 2;
    a[1] *= 2;
    d = distance(p, a);
    a = sub(p, a);
    a = normalize(a);
    a[0] /= d;
    a[1] /= d;
    s = Math.sign((i % 2) -.5 );
    a[0] *= s;
    a[1] *= s;
    v = sub(v, a);
  }
  v = normalize(v);
  return {
    x: v[0],
    y: v[1]
  };
};