Hello everyone,

I have a probability model and I would like to perform a posterior predictive check in Stan using rstan package in R. But I could not define the model in generated quantities block, please help me how to generate random numbers. I have shared my model below

f(x) = \frac{{\lambda \beta }}
{{x^2 (1 - e^{ - \lambda } )}}\left\{ {1 + \alpha \left( {1 - e^{ - \beta /x} } \right)} \right\}\exp \left( { - \frac{\beta }{x} - \alpha e^{ - \beta /x} } \right)\exp \left\{ { - \lambda \left( {1 - e^{ - \beta /x} } \right)\exp ( - \alpha e^{ - \beta /x} )} \right\}{\text{ }}

```
functions{real poissonISG_lpdf(real y, real alpha, real beta, real lambda){
return log(beta)+log(lambda)- log(1 - exp(-lambda))- 2*log(y) + log(1+alpha*(1 - exp(-(beta*1/y))))-
(beta*1/y) - alpha*exp(-(beta*1/y)) -lambda*(1-exp(-(beta*1/y)))*exp(-alpha*exp(-(beta*1/y)));
}
}
data{
int N;
real y[N];
}
parameters{
real <lower=0> alpha;
real <lower=0> beta;
real <lower=0> lambda;
}
model{
for(i in 1 : N){
y[i]~ poissonISG(alpha, beta, lambda);
}
alpha~ gamma(0.5, 0.5);
beta~ gamma(0.1, 0.1);
lambda~ gamma(0.1, 0.1);
}
generated quantities{ please help}
```

my data set is

```
y <- c(1.312, 1.314, 1.479, 1.552, 1.700, 1.803, 1.861, 1.865, 1.944, 1.958,
1.966, 1.997, 2.006, 2.021, 2.027, 2.055,2.063, 2.098, 2.14, 2.179, 2.224, 2.240,
2.253, 2.270, 2.272, 2.274, 2.301, 2.301, 2.359, 2.382, 2.382, 2.426,2.434, 2.435,
2.478, 2.490, 2.511, 2.514, 2.535, 2.554, 2.566, 2.57, 2.586, 2.629, 2.633, 2.642,
2.648, 2.684,2.697, 2.726, 2.770, 2.773, 2.800, 2.809, 2.818, 2.821, 2.848, 2.88,
2.954, 3.012, 3.067, 3.084, 3.090, 3.096,3.128, 3.233, 3.433, 3.585, 3.585)
```