log_inv_logit.hpp

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#ifndef STAN_MATH_PRIM_FUN_LOG_INV_LOGIT_HPP
#define STAN_MATH_PRIM_FUN_LOG_INV_LOGIT_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/fun/exp.hpp>
#include <stan/math/prim/fun/log1p_exp.hpp>
#include <stan/math/prim/functor/apply_scalar_unary.hpp>
#include <cmath>
 
namespace stan {
namespace math {
 
inline double log_inv_logit(double u) {
  using std::exp;
  if (u < 0.0) {
    return u - log1p_exp(u);  // prevent underflow
  }
  return -log1p_exp(-u);
}
 
inline double log_inv_logit(int u) {
  return log_inv_logit(static_cast<double>(u));
}
 
struct log_inv_logit_fun {
  template <typename T>
  static inline auto fun(const T& x) {
    return log_inv_logit(x);
  }
};
 
template <typename T,
          require_not_nonscalar_prim_or_rev_kernel_expression_t<T>* = nullptr,
          require_not_var_matrix_t<T>* = nullptr>
inline auto log_inv_logit(const T& x) {
  return apply_scalar_unary<log_inv_logit_fun, T>::apply(x);
}
 
}  // namespace math
}  // namespace stan
 
#endif