bdrate caculation get weired results

[vacing]

    ref_br      = [5012.39, 4012.23, 3014.7, 2014.65]
    ref_metric  = [99.97751, 99.91607, 99.51432, 96.622]
    main_br     = [5096.02, 4000.03, 3067.89, 2054.35]
    main_metric = [99.98146, 99.94996, 99.66744, 97.1181]

    bd = BD_RATE(ref_br, ref_metric, main_br, main_metric)
    print(bd) # 100421.22666772884

python 3.8.5
numpy 1.24.2
scipy 1.10.1

[vacing]

it seems normal when I set piecewis=1