hypergeometric_rng.hpp

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#ifndef STAN_MATH_PRIM_PROB_HYPERGEOMETRIC_RNG_HPP
#define STAN_MATH_PRIM_PROB_HYPERGEOMETRIC_RNG_HPP
 
#include <stan/math/prim/meta.hpp>
#include <boost/math/distributions/hypergeometric.hpp>
 
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/prob/uniform_rng.hpp>
 
namespace stan {
namespace math {
 
template <class RNG>
inline int hypergeometric_rng(int N, int a, int b, RNG& rng) {
  using boost::variate_generator;
  using boost::math::hypergeometric_distribution;
  static constexpr const char* function = "hypergeometric_rng";
  check_bounded(function, "Draws parameter", value_of(N), 0, a + b);
  check_positive(function, "Draws parameter", N);
  check_positive(function, "Successes in population parameter", a);
  check_positive(function, "Failures in population parameter", b);
 
  hypergeometric_distribution<> dist(b, N, a + b);
 
  double u = uniform_rng(0.0, 1.0, rng);
  int min = 0;
  int max = a - 1;
  while (min < max) {
    int mid = (min + max) / 2;
    if (cdf(dist, mid + 1) > u) {
      max = mid;
    } else {
      min = mid + 1;
    }
  }
  return min + 1;
}
 
}  // namespace math
}  // namespace stan
#endif