Zero-inflated Poisson Log Probability Mass Function Stan Code

Stan code for the zero-inflated Poisson distribution's log probability mass function.

Examples

cat(zi_poisson_lpmf_stan[["source_code"]])
#> // The log probability mass at x, given lambda and pi.
#> // lambda is the (non-negative) mean of the poisson distribution.
#> // pi is the amount of zero-inflation, which should lie within the range [0, 1].
#> real zi_poisson_lpmf(int n, real lambda, real pi) {
#> 
#>     if (pi < 0 || pi > 1) {
#>       reject("pi should be in [0, 1]; pi=", pi);
#>     }
#> 
#>     // TODO: Would this be more efficient if it used log_sum_exp?
#>     return log(pi * (n == 0) + (1 - pi) * exp(poisson_lpmf(n | lambda)));
#> }