hypergeometric_pFq.hpp

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#ifndef STAN_MATH_REV_FUN_HYPERGEOMETRIC_PFQ_HPP
#define STAN_MATH_REV_FUN_HYPERGEOMETRIC_PFQ_HPP
 
#include <stan/math/rev/core.hpp>
#include <stan/math/rev/meta.hpp>
#include <stan/math/prim/fun/as_column_vector_or_scalar.hpp>
#include <stan/math/prim/fun/grad_pFq.hpp>
#include <stan/math/prim/fun/hypergeometric_pFq.hpp>
 
namespace stan {
namespace math {
 
template <typename Ta, typename Tb, typename Tz,
          require_all_vector_t<Ta, Tb>* = nullptr,
          require_return_type_t<is_var, Ta, Tb, Tz>* = nullptr>
inline var hypergeometric_pFq(Ta&& a, Tb&& b, Tz&& z) {
  constexpr bool grad_a = is_autodiff_v<Ta>;
  constexpr bool grad_b = is_autodiff_v<Tb>;
  constexpr bool grad_z = is_autodiff_v<Tz>;
  auto arena_a = to_arena(as_column_vector_or_scalar(std::forward<Ta>(a)));
  auto arena_b = to_arena(as_column_vector_or_scalar(std::forward<Tb>(b)));
  auto pfq_val
      = hypergeometric_pFq(value_of(arena_a), value_of(arena_b), value_of(z));
  return make_callback_var(
      pfq_val, [arena_a, arena_b, z, pfq_val](auto& vi) mutable {
        auto grad_tuple = grad_pFq<grad_a, grad_b, grad_z>(
            pfq_val, arena_a.val(), arena_b.val(), value_of(z));
        if constexpr (grad_a) {
          arena_a.adj() += vi.adj() * std::get<0>(grad_tuple);
        }
        if constexpr (grad_b) {
          arena_b.adj() += vi.adj() * std::get<1>(grad_tuple);
        }
        if constexpr (grad_z) {
          z.adj() += vi.adj() * std::get<2>(grad_tuple);
        }
      });
}
}  // namespace math
}  // namespace stan
#endif