code: def get_MD_VDS(tail_check_max, vds):
      
      if tail_check_max == 0 or numpy.isnan(tail_check_max):
          return float('nan')
      MD_VDS = (old_div(tail_check_max, vds)) * 100
      return MD_VDS
docs: input: tail_check_max, vector difference sum
      output: MD_VDS