bessel_first_kind.hpp

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#ifndef STAN_MATH_REV_FUN_BESSEL_FIRST_KIND_HPP
#define STAN_MATH_REV_FUN_BESSEL_FIRST_KIND_HPP
 
#include <stan/math/rev/meta.hpp>
#include <stan/math/rev/core.hpp>
#include <stan/math/prim/fun/bessel_first_kind.hpp>
 
namespace stan {
namespace math {
 
inline var bessel_first_kind(int v, const var& a) {
  auto ret_val = bessel_first_kind(v, a.val());
  auto precomp_bessel
      = v * ret_val / a.val() - bessel_first_kind(v + 1, a.val());
  return make_callback_var(ret_val,
                           [precomp_bessel, a](const auto& vi) mutable {
                             a.adj() += vi.adj_ * precomp_bessel;
                           });
}
 
template <typename T1, typename T2, require_st_integral<T1>* = nullptr,
          require_eigen_t<T2>* = nullptr>
inline auto bessel_first_kind(const T1& v, const var_value<T2>& a) {
  auto ret_val = bessel_first_kind(v, a.val()).array().eval();
  auto v_map = as_array_or_scalar(v);
  auto precomp_bessel
      = to_arena(v_map * ret_val / a.val().array()
                 - bessel_first_kind(v_map + 1, a.val().array()));
  return make_callback_var(
      ret_val.matrix(), [precomp_bessel, a](const auto& vi) mutable {
        a.adj().array() += vi.adj().array() * precomp_bessel;
      });
}
 
}  // namespace math
}  // namespace stan
#endif