docs: def calc_std(c0, c1=[]):
      """ Calculates the variance of the data."""
      if c1 == []:
          return numpy.std(c0, 0)
      prop = float(len(c0)) / float(len(c1))
      if prop < 1:
          p0 = int(math.ceil(1 / prop))
          p1 = 1
      else:
          p0 = 1
          p1 = int(math.ceil(prop))
      return numpy.std(numpy.vstack(p0 * [c0] + p1 * [c1]), 0)