code: def covar(self, bessel=True):
          
          if bessel:
              return self.Mxy/ (self.w-1)
          else:
              return self.Mxy / self.w
docs: Return covariance matrix:
  
          Parameters:
          -----------
          bessel : bool, optional, default=True
              Use Bessel's correction in order to
              obtain an unbiased estimator of sample covariances.