Error messgae in JAGS when defining constraints for priors Attempt to redefine node

Question

I am trying to sample from prior distributions and constrain some of the sums and differences to be greater than 0, however, when I run this code that usually works in OpenBugs/WinBugs, I get the following error 'Attempt to redefine node '. I was wondering if there is any possible way to define my constraints in order to prevent this error from occurring. Any help would be massively appreciated.

Thanks

S[1,1] ~ dbeta(8.10, 32.81)
d[1,1] ~ dbeta(4.36, 32.61)
d[1,2] ~ dnorm(0.097, 250)
d[2,2] ~ dbeta(2.23, 20.10)

Z1 <- 1
Z1 ~ dbern(constraint) 

#Constraints

constraint <- step(S[1,1] + d[1,2])*
                       step(1 - S[1,1] - d[1,2])*
                       step(S[1,1] - d[1,1])*
                       step(S[1,1] + d[1,2] - d[2,2])

Answer 1

One way would be to define Z1as 1 in the data and take it out of the model. Then, you can leave in the Z1~dbern(constraint) in the model.