# Help with Poisson model

**URL:** <https://discourse.mc-stan.org/t/help-with-poisson-model/3352>\
**Category:** Modeling\
**Tags:** loo\
**Created:** [February 19, 2018, 6:05pm UTC](https://discourse.mc-stan.org/t/help-with-poisson-model/3352 "2018-02-19T18:05:35Z")\
**Posts on this page:** 1\
**Showing post:** 42

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**Author:** ![bbbales2](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/bbbales2/32/77_2.png) [@bbbales2](https://discourse.mc-stan.org/u/bbbales2)\
**Post date:** [March 2, 2018, 1:05am UTC](https://discourse.mc-stan.org/t/help-with-poisson-model/3352/42 "2018-03-02T01:05:49Z")

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Yegads, well, if you want to figure out how to fix that C++ there’s a very small chance that we’d see an interesting behavior :P. Long shot, but do you have the latest Rstan?

I’m honestly stumped on this. Without the specific data/model causing the problem, it’s hard to do anything other than make undirected guesses.

If it’s absolutely commenting and uncommenting this that causes the problem:

```stan
for (it in 1:I * T) {
  y_sim[it] = poisson_log_rng(y_hat[it]);
}

```

then I’m stumped! It doesn’t look like you’re using any fixed seeds or anything?

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