rm(list = ls())
# Set working directory and read posterior samples
setwd("c:\\E-drive\\Books\\LOGLIN3\\BAYES\\")
load("post-samp.Rda")
# respecify number of iterates
iterates=length(beta[1,])
# respecify prior parameters
a <- c( 1, .577 )
b <- c( .577, 1 )
# define logit function
logit <- function(p)
{
lg = log(p/(1-p))
return(lg)}
# Sample from prior ptildes and transform to betas
prior_p1 <- rbeta(iterates, a[1], b[1])
prior_p2 <- rbeta(iterates, a[2], b[2])
prior_beta1 <-
   (75/20) * logit( prior_p1 ) - (55/20) * logit( prior_p2 )
prior_beta2 <-
   (1/20) * logit( prior_p2 ) - (1/20) * logit( prior_p1 )

# Save prior and posterior samples
# for later use in a data frame.
beta_frame <- data.frame( cbind( prior_beta1,
                     prior_beta2, beta[1,], beta[2,] ) )
names( beta_frame ) <-
  c( "prior_beta1", "prior_beta2",
          "posterior_beta1", "posterior_beta2" )
save(beta_frame,file="beta-samples.Rda")