log_softmax.hpp

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#ifndef STAN_MATH_PRIM_FUN_LOG_SOFTMAX_HPP
#define STAN_MATH_PRIM_FUN_LOG_SOFTMAX_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/fun/log_sum_exp.hpp>
#include <stan/math/prim/fun/to_ref.hpp>
#include <stan/math/prim/functor/apply_vector_unary.hpp>
 
namespace stan {
namespace math {
 
template <typename Container, require_st_arithmetic<Container>* = nullptr,
          require_container_t<Container>* = nullptr>
inline auto log_softmax(const Container& x) {
  check_nonzero_size("log_softmax", "v", x);
  return make_holder(
      [](const auto& a) {
        return apply_vector_unary<ref_type_t<Container>>::apply(
            a, [](const auto& v) { return v.array() - log_sum_exp(v); });
      },
      to_ref(x));
}
 
}  // namespace math
}  // namespace stan
#endif