to_var_value.hpp

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#ifndef STAN_MATH_REV_FUN_TO_VAR_VALUE_HPP
#define STAN_MATH_REV_FUN_TO_VAR_VALUE_HPP
 
#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/rev/core.hpp>
#include <stan/math/rev/core/arena_matrix.hpp>
#include <stan/math/rev/core/reverse_pass_callback.hpp>
 
namespace stan {
namespace math {
 
template <typename T, require_eigen_vt<is_var, T>* = nullptr>
inline var_value<
    Eigen::Matrix<double, T::RowsAtCompileTime, T::ColsAtCompileTime>>
to_var_value(const T& a) {
  arena_matrix<plain_type_t<T>> a_arena = a;
  var_value<promote_scalar_t<double, T>> res(a_arena.val());
  reverse_pass_callback(
      [res, a_arena]() mutable { a_arena.adj() += res.adj(); });
  return res;
}
 
template <typename T, require_var_t<T>* = nullptr>
inline T to_var_value(T&& a) {
  return std::forward<T>(a);
}
 
template <typename T>
inline auto to_var_value(const std::vector<T>& a) {
  std::vector<decltype(to_var_value(std::declval<T>()))> out;
  out.reserve(a.size());
  for (size_t i = 0; i < a.size(); ++i) {
    out.emplace_back(to_var_value(a[i]));
  }
  return out;
}
 
}  // namespace math
}  // namespace stan
 
#endif