docs: def disk_pick_polar(n=1, rng=None):
      """Return vectors uniformly picked on the unit disk.
      The unit disk is the space enclosed by the unit circle.
      Vectors are in a polar representation.
  
      Parameters
      ----------
      n: integer
          Number of points to return.
  
      Returns
      -------
      r: array, shape (n, 2)
          Sample vectors.
      """
      if rng is None:
          rng = np.random
      a = np.zeros([n, 2], dtype=np.float)
      a[:, 0] = np.sqrt(rng.uniform(size=n))
      a[:, 1] = rng.uniform(0.0, 2.0 * np.pi, size=n)
      return a