Hi,

I am new to the Bayesian modelling world, and this is the first time I am using pystan for a Recommender Systems project.

I am trying to model user clicks using a simple Bayesian model with clicks being modelled as a binomial variable (for each user, item pairs). The number of impressions is the total number of trails for a given (user, item) pair and ‘click’ is a success.

The corresponding pystan code is as follows:

```
non_hierarchical_model = """
data{
int U;
int I;
int N;
int<lower=1> click[N];
int<lower=1> impressions[N];
int<lower=0> prod_idx[N];
int<lower=0> user_idx[N];
}
parameters {
real<lower=0, upper=1> Alpha[I];
real<lower=0, upper=1> Beta[I];
real<lower=0, upper=1> Alpha1[U];
real<lower=0, upper=1> Beta1[U];
real<lower=0, upper=1> obs[N];
real<lower=0, upper=1> rel[N];
}
model{
for (n in 1:N) {
Alpha[prod_idx[n]] ~ beta(0.5, 0.5);
Beta[prod_idx[n]] ~ beta(0.5, 0.5);
Alpha1[user_idx[n]] ~ beta(0.5, 0.5);
Beta1[user_idx[n]] ~ beta(0.5, 0.5);
obs[n] ~ beta(Alpha[prod_idx[n]], Beta[prod_idx[n]]);
rel[n] ~ beta(Alpha1[user_idx[n]], Beta1[user_idx[n]]);
click[n] ~ binomial_logit(impressions[n], obs[n] * rel[n]);
}
}
"""
```

I am trying to model clicks as Observation * Relevance, where observation is defined for items and relevance is defined for users, and the final click probability is the product of the two.

When I try to sample from this model, I am getting the following error:

```
RuntimeError: Exception during call to services function: `BrokenProcessPool('A process in the process pool was terminated abruptly while the future was running or pending.')`, traceback: `[' File "/ivi/ilps/personal/sgupta/anaconda3/envs/pystan/lib/python3.7/site-packages/httpstan/services_stub.py", line 153, in call\n future.result()\n']`
```

I have tried putting the code inside “**main**” block as per some discussion, but no success. Is it because of some modelling issue or something else all together?