Fig7.7 <- function(n = 128)
{
#  postscript(file = "Fig7.7.ps", height = 6.5, width = 6.5, horiz = F)
  par(mfrow = c(2, 2), mar = c(1.5, 1.5, 1.5, 0.5), mgp = c(5, 0.4, 0))
  rs <- c(57, 14, 55, 51, 30, 0, 53, 44, 34, 53, 49, 2)
  .Random.seed <- rs
  y1 <- rnorm(n)
  y2 <- arima.sim(n, model = list(ar = 0.5))
  y3 <- arima.sim(n, model = list(ar = -0.5))
  y4 <- arima.sim(n, model = list(ar = c(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
                                      0, 0.5)))
  omega <- ((0:(n/2)) * 2 * pi)/n
  p1 <- spec.pgram(y1)
  p2 <- spec.pgram(y2)
  p3 <- spec.pgram(y3)
  p4 <- spec.pgram(y4)
  plot(omega, 10^(p1$spec/10), type = "l")
  mtext("White noise", side = 3, line = 0.1)
  plot(omega, 10^(p2$spec/10), type = "l")
  mtext("AR(1), r = 0.5", side = 3, line = 0.1)
  plot(omega, 10^(p3$spec/10), type = "l")
  mtext("AR(1), r = -0.5", side = 3, line = 0.1)
  plot(omega, 10^(p4$spec/10), type = "l")
  mtext("Seasonal time series", side = 3, line = 0.1)
#  graphics.off()
  NULL
}