#example pag 50 gelman book: estimating a rate from poisson data: an idealized example
exposure_function(w=0){
  if (w == 1) postscript("/home/biostats/fdominic/course/exposure.ps")
  par(mfrow=c(2,1))
  prior.theta_rgamma(1000,3)/5
  hist(prior.theta,nclass=50,xlab="theta",ylab="prior",yaxt="n",
       density=-1,prob=T,cex=2 ,xlim=c(0,3))
  abline(v=mean(prior.theta),lwd=2)
  mtext("PRIOR",side=3)
  posterior.theta_rgamma(1000,6)/7
  hist(posterior.theta,nclass=50,xlab="theta",ylab="posterior",yaxt="n",
       density=-1,prob=T,cex=2,xlim=c(0,3))
  abline(v=mean(posterior.theta),lwd=2)
  mtext("POSTERIOR",side=3)
  ppp_ sum(posterior.theta>1)/1000
  par(oma=c(0,0,0,0))
  par(mfrow=c(1,1))
  if (w == 1) dev.off()
}