04.01.2013 Views

Springer - Read

Springer - Read

Springer - Read

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

184 Chapter 6 Nonstationary and Seasonal Time Series Models<br />

ACF<br />

-0.2 0.0 0.2 0.4 0.6 0.8 1.0<br />

Figure 6-5<br />

The sample ACF of the<br />

0 10 20 30 40<br />

series {Yt } in Figure 6.4. Lag<br />

(6.1.4), which has very similar coefficients but for which φ ∗ has all of its zeros outside<br />

the unit circle. In either case, however, if it is possible by differencing to generate a<br />

series with rapidly decaying sample ACF, then the differenced data set can be fitted<br />

by a low-order ARMA process whose autoregressive polynomial φ ∗ has zeros that<br />

are comfortably outside the unit circle. This means that the fitted parameters will<br />

be well away from the boundary of the allowable parameter set. This is desirable<br />

PACF<br />

-0.2 0.0 0.2 0.4 0.6 0.8 1.0<br />

Figure 6-6<br />

The sample PACF of the<br />

0 10 20 30 40<br />

series {Yt } in Figure 6.4. Lag

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!