log_sum_exp.hpp

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#ifndef STAN_MATH_OPENCL_PRIM_LOG_SUM_EXP_HPP
#define STAN_MATH_OPENCL_PRIM_LOG_SUM_EXP_HPP
#ifdef STAN_OPENCL
#include <stan/math/opencl/kernel_generator.hpp>
#include <stan/math/opencl/prim/sum.hpp>
#include <stan/math/opencl/ref_type.hpp>
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/err/check_matching_sizes.hpp>
#include <stan/math/prim/fun/constants.hpp>
 
namespace stan {
namespace math {
 
template <typename T,
          require_all_kernel_expressions_and_none_scalar_t<T>* = nullptr>
inline double log_sum_exp(const T& a) {
  using std::log;
  if (a.size() == 0) {
    return NEGATIVE_INFTY;
  }
  if (stan::internal::is_trivial_kg_expression<T>::value) {
    double a_max = from_matrix_cl(max_2d(a)).maxCoeff();
    if (!std::isfinite(a_max)) {
      return a_max;
    }
    return a_max + log(sum(exp(a - a_max)));
  } else {
    matrix_cl<double> a_eval;
    matrix_cl<double> a_max_cl;
    results(a_eval, a_max_cl) = expressions(a, max_2d(a));
    double a_max = from_matrix_cl(a_max_cl).maxCoeff();
    if (!std::isfinite(a_max)) {
      return a_max;
    }
    return a_max + log(sum(exp(a_eval - a_max)));
  }
}
 
}  // namespace math
}  // namespace stan
 
#endif
#endif