\frametitle {R code used to estimate the covariance function}
\begin{verbatim}
par(mfrow=c(3,1),mar=c(4,4,1,2))
acf(y1,lag.max=100,type='cov')
lines(times,exp(-times/alpha1))

acf(y2,lag.max=100,type='cov')
lines(times,exp(-times/alpha2),col=2)

acf(y3,lag.max=100,type='cov')
lines(times,exp(-times/alpha3),col=3)
\end{verbatim}