Example: Upsampling by 2

For $N=2$ , upsampling (stretching) by 2 can be expressed as
$y=[x_0,0,x_1,0,\ldots]$ , so that

$$Y(z) \eqsp X(z^2) \eqsp \hbox{\sc Repeat}_2(X),$$ (12.2)

as discussed more fully in §2.3.11.