XS中MACD選股失敗

想要找出difValue向下突破o的股票，但是這個程式總是失敗。請問誰知道bug在哪裡嗎？

input: FastLength(26), SlowLength(12);

variable: price(0),DIF(0);

price = WeightedClose();

DIF = XAverage(price, FastLength) - XAverage(price, SlowLength);

if DIF[1] > 0 and DIF <= 0

then ret =1;