大家帮忙看一下 程序问题出在哪儿了呢？
为什么我的预测值是平的呢？谢谢~

beta=c(-0.266629158,-0.300429234,-0.242163858,-0.292667173,-0.263094949,-0.097495396,-0.115491818,-0.050959309,-0.065439934,
0.024011574,0.11187841,0.103109854,0.287722583,0.417265713,0.246244017,0.504138678)
ts.beta=ts(beta,frequency=1,start=c(1994))
fit=arima(ts.beta, order = c(1,1,0),method="ML")
pred.fit=predict(fit, n.ahead =20)
total=c(beta,pred.fit$pred)
total.ts=ts(total,frequency=1,start=c(1994))
plot(total.ts,type='b')