hypergeometric_1F0.hpp

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#ifndef STAN_MATH_FWD_FUN_HYPERGEOMETRIC_1F0_HPP
#define STAN_MATH_FWD_FUN_HYPERGEOMETRIC_1F0_HPP
 
#include <stan/math/fwd/core.hpp>
#include <stan/math/fwd/meta.hpp>
#include <stan/math/fwd/fun/log1m.hpp>
#include <stan/math/fwd/fun/inv.hpp>
#include <stan/math/fwd/fun/value_of.hpp>
#include <stan/math/prim/fun/hypergeometric_1F0.hpp>
 
namespace stan {
namespace math {
 
template <typename Ta, typename Tz, typename FvarT = return_type_t<Ta, Tz>,
          require_all_stan_scalar_t<Ta, Tz>* = nullptr,
          require_any_fvar_t<Ta, Tz>* = nullptr>
inline FvarT hypergeometric_1F0(const Ta& a, const Tz& z) {
  partials_type_t<Ta> a_val = value_of(a);
  partials_type_t<Tz> z_val = value_of(z);
  FvarT rtn = FvarT(hypergeometric_1F0(a_val, z_val), 0.0);
  if constexpr (is_autodiff_v<Ta>) {
    rtn.d_ += a.d() * -rtn.val() * log1m(z_val);
  }
  if constexpr (is_autodiff_v<Tz>) {
    rtn.d_ += z.d() * rtn.val() * a_val * inv(1 - z_val);
  }
  return rtn;
}
 
}  // namespace math
}  // namespace stan
#endif