model {
  for (i in 1:n) {
     mean[i] <- a*day[i]*exp(-b*day[i])
     rate[i] <- shape/mean[i]
     titer[i] ~ dgamma(shape,rate[i])
  }
## priors
a ~ dgamma(0.1,0.1)
b ~ dgamma(0.1,0.1)
shape ~ dgamma(0.1,0.01)
}