求救！！！   如题，用arima做的模型出来时一条直线，普通的arima（1,1,1）模型
代码：
estim1 <- arima(x=da3, order = c(1,1,1))
predict(estim1,n.ahead=10,se.set=T)

结果：
$pred
Time Series:
Start = 1099
End = 1108
Frequency = 1
[1] 1.818600 1.818567 1.818569 1.818569 1.818569 1.818569 1.818569 1.818569
[9] 1.818569 1.818569

$se
Time Series:
Start = 1099
End = 1108
Frequency = 1
[1] 0.004082645 0.006346266 0.007962979 0.009304444 0.010475420 0.011528066
[7] 0.012492325 0.013387310 0.014226101 0.015018116


预测数据全一样是咋么回事啊？求高人速答，万分感谢！！！！！！！