norm2.hpp

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#ifndef STAN_MATH_REV_FUN_NORM2_HPP
#define STAN_MATH_REV_FUN_NORM2_HPP
 
#include <stan/math/rev/meta.hpp>
#include <stan/math/rev/core.hpp>
#include <stan/math/rev/core/typedefs.hpp>
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/Eigen.hpp>
 
namespace stan {
namespace math {
 
template <typename T, require_eigen_vector_vt<is_var, T>* = nullptr>
inline var norm2(const T& v) {
  arena_t<T> arena_v = v;
  var res = norm2(arena_v.val());
  reverse_pass_callback([res, arena_v]() mutable {
    arena_v.adj().array() += res.adj() * (arena_v.val().array() / res.val());
  });
  return res;
}
 
template <typename T, require_var_matrix_t<T>* = nullptr>
inline var norm2(const T& v) {
  return make_callback_vari(norm2(v.val()), [v](const auto& res) mutable {
    v.adj().array() += res.adj() * (v.val().array() / res.val());
  });
}
 
}  // namespace math
}  // namespace stan
#endif