### Poisson regression

An example of a simple poisson regression being used to estimate the abundance of a species along a number of environmental gradients.

#### data
```{r data_poisson, highlight = FALSE}
# make fake data
n_env <- 3
n_sites <- 20

# n_sites x n_env matrix of environmental variables
env <- matrix(rnorm(n_sites * n_env), nrow = n_sites) 
# n_sites observations of species abundance
occupancy <- rpois(n_sites, 5) 
```

#### greta code
```{r poisson_greta}
alpha <- normal(0, 10)
beta <- normal(0, 10, dim = n_env)
linear_predictor <- alpha + env %*% beta
lambda <- exp(linear_predictor)
distribution(occupancy) <- poisson(lambda)
```
