model
   {
      for( i in 1 : N ) {
         Y[i] ~ dnorm(mu[i], tau)
         mu[i] <- alpha - beta * pow(gamma,x[i])         
      }
      alpha ~ dnorm(0.0, 1.0E-6)
      beta ~ dnorm(0.0, 1.0E-6)
      gamma ~ dunif(0.5, 1.0)
      tau ~ dgamma(0.001, 0.001)
      sigma <- 1 / sqrt(tau)
      U3 <- logit(gamma)   
   }