code: def rn(x, af, rate):
      
      (taus,devs,errs,ns) = at.adev(x,taus=[af*rate], data_type='phase', rate=rate) 
      oadev_x = devs[0]
      (mtaus,mdevs,errs,ns) = at.mdev(x,taus=[af*rate], data_type='phase', rate=rate)
      mdev_x = mdevs[0]
      rn = pow(mdev_x/oadev_x,2)
      return rn
docs: R(n) ratio for noise identification
      
          ration of MVAR to AVAR