为什么AverageFC函数计算出来的是无效值？

写了个DMI指标的函数，用于计算PDI、MDI、ADX的值。打印出ADX的值为“ADX=N/A”,附源码如下： Params NumericRef PDI; NumericRef MDI; Numeric Length1(28); Numeric Length2(6); Vars Numeric TR; Numeric HD; Numeric LD; Numeric DMP; Numeric DMM; Numeric ADX; Begin TR = Summation(Max(Max(High - Low,Abs(High - Close[1])),Abs(Low - Close[1])),Length1); HD = High - High[1]; LD = Low[1] - Low; DMP = Summation(IIF(HD > 0 && HD > LD,HD,0),Length1); DMM = Summation(IIF(LD > 0 && LD > HD,LD,0),Length1); PDI = DMP * 100 / TR; MDI = DMM * 100 / TR; ADX = AverageFC(Abs(MDI - PDI) / (MDI + PDI) * 100,Length2); print("ADX="+text(ADX)); return 1; End