def norm_time(astr)
      idx = astr > 13 ? astr - 2 : astr
      jd_start = @bin[:jds_cheb][0]
      tc = (@jd - jd_start) / @bin[:sss][2].to_f
      temp = tc * @bin[:ipts][idx - 1][2]
      idx = (temp - tc.floor).floor         # サブ区間のインデックス
      tc = (temp % 1.0 + tc.floor) * 2 - 1  # チェビシェフ時間
      return [tc, idx]
    rescue => e
      raise
    end
def norm_time(astr)
      idx = astr > 13 ? astr - 2 : astr
      jd_start = @bin[:jds_cheb][0]
      tc = (@jd - jd_start) / @bin[:sss][2].to_f
      temp = tc * @bin[:ipts][idx - 1][2]
      idx = (temp - tc.floor).floor         # サブ区間のインデックス
      tc = (temp % 1.0 + tc.floor) * 2 - 1  # チェビシェフ時間
      return [tc, idx]
    rescue => e
      raise
    end
=========================================================================
 Time normalization, sub-period's index calculation for Chebyshev's Polynomial

 @param:  astr (= atronomical no)
 @return: [chebyshev-time, sub-index]
=========================================================================