Ok. I’m trying to generate priors to help tune a model that is misbehaving. I’m using this code:

```
data{
int<lower=0> N; // Total number of rows
}
generated quantities{
real<lower=0> Tau0 = cauchy_rng(0, 2);
real<lower=0> Tau = cauchy_rng(0, 2);
real<lower=0> sd_oc = cauchy_rng(0, 1);
real<lower=0> sd_dom = cauchy_rng(0, 1);
real<lower=0> sd0_dom = cauchy_rng(0, 1);
real beta_oc = normal_rng(0, sd_oc);
real beta_dom = normal_rng(0, sd_dom);
real beta0_dom = normal_rng(0, sd0_dom);
real Zbeta0_ind = normal_rng(0,1);
real Zbeta_ind = normal_rng(0,1);
}
```

So I’m running this with this line:

```
fit2 <- stan(file='gen_priors.stan', data=datalist,
iter=1, warmup=0, chains=1,
seed=4838282, algorithm="Fixed_param")
```

The model compiles ok but then I’m getting this error:

```
SAMPLING FOR MODEL 'gen_priors' NOW (CHAIN 1).
Chain 1: Iteration: 1 / 1 [100%] (Sampling)
Chain 1: Exception: model12a285c27a9d0_gen_priors_namespace::write_array: Tau is -7.68902, but must be greater than or equal to 0 (in 'model12a285c27a9d0_gen_priors' at line 15)
Chain 1:
Chain 1: Elapsed Time: 0 seconds (Warm-up)
Chain 1: 0.000169 seconds (Sampling)
Chain 1: 0.000169 seconds (Total)
Chain 1:
[1] "Error in sampler$call_sampler(args_list[[i]]) : "
[2] " Exception: model12a285c27a9d0_gen_priors_namespace::write_array: Tau is -7.68902, but must be greater than or equal to 0 (in 'model12a285c27a9d0_gen_priors' at line 15)"
error occurred during calling the sampler; sampling not done
```

Ehhh, whats goin on here then? Why is Tau negative when I’ve set <lower=0> ?