positive_constrain.hpp

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#ifndef STAN_MATH_PRIM_CONSTRAINT_POSITIVE_CONSTRAIN_HPP
#define STAN_MATH_PRIM_CONSTRAINT_POSITIVE_CONSTRAIN_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/fun/exp.hpp>
#include <stan/math/prim/fun/sum.hpp>
#include <cmath>
 
namespace stan {
namespace math {
 
template <typename T>
inline auto positive_constrain(T&& x) {
  return exp(std::forward<T>(x));
}
 
template <typename T, typename S>
inline auto positive_constrain(T&& x, S& lp) {
  auto&& x_ref = to_ref(std::forward<T>(x));
  lp += sum(x_ref);
  return exp(std::forward<decltype(x_ref)>(x_ref));
}
 
template <bool Jacobian, typename T, typename Lp,
          require_not_std_vector_t<T>* = nullptr,
          require_convertible_t<return_type_t<T>, Lp>* = nullptr>
inline auto positive_constrain(T&& x, Lp& lp) {
  if constexpr (Jacobian) {
    return positive_constrain(std::forward<T>(x), lp);
  } else {
    return positive_constrain(std::forward<T>(x));
  }
}
 
template <bool Jacobian, typename T, typename Lp,
          require_std_vector_t<T>* = nullptr,
          require_convertible_t<return_type_t<T>, Lp>* = nullptr>
inline auto positive_constrain(T&& x, Lp& lp) {
  return apply_vector_unary<T>::apply(std::forward<T>(x), [&lp](auto&& v) {
    return positive_constrain<Jacobian>(std::forward<decltype(v)>(v), lp);
  });
}
 
}  // namespace math
}  // namespace stan
 
#endif