discrete_range_lccdf.hpp

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#ifndef STAN_MATH_PRIM_PROB_DISCRETE_RANGE_LCCDF_HPP
#define STAN_MATH_PRIM_PROB_DISCRETE_RANGE_LCCDF_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/constants.hpp>
#include <stan/math/prim/fun/inv.hpp>
#include <stan/math/prim/fun/log.hpp>
#include <stan/math/prim/fun/max_size.hpp>
#include <stan/math/prim/fun/scalar_seq_view.hpp>
#include <stan/math/prim/fun/size_zero.hpp>
#include <cmath>
 
namespace stan {
namespace math {
 
template <typename T_y, typename T_lower, typename T_upper>
double discrete_range_lccdf(const T_y& y, const T_lower& lower,
                            const T_upper& upper) {
  static constexpr const char* function = "discrete_range_lccdf";
  check_consistent_sizes(function, "Lower bound parameter", lower,
                         "Upper bound parameter", upper);
  check_greater_or_equal(function, "Upper bound parameter", upper, lower);
 
  if (size_zero(y, lower, upper)) {
    return 0;
  }
 
  scalar_seq_view<T_y> y_vec(y);
  scalar_seq_view<T_lower> lower_vec(lower);
  scalar_seq_view<T_upper> upper_vec(upper);
  size_t N = max_size(y, lower, upper);
 
  for (size_t n = 0; n < N; ++n) {
    const int y_dbl = y_vec[n];
    if (y_dbl >= upper_vec[n]) {
      return LOG_ZERO;
    }
  }
 
  double ccdf(0.0);
  for (size_t n = 0; n < N; n++) {
    const int y_dbl = y_vec[n];
    if (y_dbl >= lower_vec[n]) {
      const int lower_dbl = lower_vec[n];
      const int upper_dbl = upper_vec[n];
      ccdf += log(upper_dbl - y_dbl) - log(upper_dbl - lower_dbl + 1);
    }
  }
  return ccdf;
}
 
}  // namespace math
}  // namespace stan
#endif