Can you please fix why my code produces an error??

```
data {
int<lower=1> n; // Number of data
int<lower=1> p; // Number of covariates
matrix[n,p] X; // n-by-p design matrix
real y[n]; // n-dimensional response vector
}
parameters {
vector[p] beta;
vector<lower=0>[p] lambda_sq;
vector<lower=0>[p] omega;
real<lower=0> tau_sq;
real<lower=0> eta;
real<lower=0> sigma;
}
transformed parameters {
vector[n] theta ;
theta = X * beta;
}
model {
// Origianal horseshoe by carvalho + Parameter expansion on half-Cauchy
//lambda ~ cauchy(0, 1) is equivalent with;
omega ~ inv_gamma(1 / 2, 1);
lambda_sq ~ inv_gamma(1 / 2, 1 ./ omega);
//tau ~ cauchy(0, 1) is equivalent with;;
eta ~ inv_gamma(1 / 2, 1);
tau_sq ~ inv_gamma(1 / 2, 1 / eta);
beta ~ normal(0, sigma * sqrt(tau_sq) * sqrt(lambda_sq) );
y ~ normal(theta, sigma);
}
```