def outer_n(n):
  return np.roll(np.arange(n) - n/2, (n + 1) / 2)
Validates that we aren't trying to do a query like
dataset/ETHPy150Open breuderink/eegtools/eegtools/spatfilt.py/outer_n--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.5/django/db/models/query.py/ValuesQuerySet._prepare