code: def __distance_valid(self, g0, g1, p):
          
          dist = np.sqrt((g1.x - g0.x) ** 2 +
                      (g1.y - g0.y) ** 2)
          return dist >= p.min_separation
docs: Returns true if the distance between the (x,y) locations of
          two generators g0 and g1 is greater than a minimum separation.
  
          Can be extended easily to support other criteria.