dirichlet_multinomial_rng.hpp

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#ifndef STAN_MATH_PRIM_PROB_DIRICHLET_MULTINOMIAL_RNG_HPP
#define STAN_MATH_PRIM_PROB_DIRICHLET_MULTINOMIAL_RNG_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/to_ref.hpp>
#include <stan/math/prim/prob/dirichlet_rng.hpp>
#include <stan/math/prim/prob/multinomial_rng.hpp>
#include <vector>
 
namespace stan {
namespace math {
 
template <class RNG>
inline std::vector<int> dirichlet_multinomial_rng(
    const Eigen::Matrix<double, Eigen::Dynamic, 1>& alpha, int N, RNG& rng) {
  static const char* function = "dirichlet_multinomial_rng";
  const auto& alpha_ref = to_ref(alpha);
  check_positive_finite(function, "prior size variable", alpha_ref);
  check_nonnegative(function, "number of trials variables", N);
 
  // special case N = 0 would lead to an exception thrown by multinomial_rng
  if (N == 0) {
    return std::vector<int>(alpha.size(), 0);
  }
 
  // sample a simplex theta from the Dirichlet distribution
  auto theta = dirichlet_rng(alpha_ref, rng);
 
  // using the simplex theta, sample from the multinomial distribution
  return multinomial_rng(theta, N, rng);
}
 
}  // namespace math
}  // namespace stan
#endif