trace.hpp

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#ifndef STAN_MATH_REV_FUN_TRACE_HPP
#define STAN_MATH_REV_FUN_TRACE_HPP
 
#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/meta.hpp>
#include <stan/math/rev/core.hpp>
#include <stan/math/rev/meta.hpp>
 
namespace stan {
namespace math {
 
template <typename T, require_rev_matrix_t<T>* = nullptr>
inline auto trace(const T& m) {
  arena_t<T> arena_m = m;
 
  return make_callback_var(arena_m.val_op().trace(),
                           [arena_m](const auto& vi) mutable {
                             arena_m.adj().diagonal().array() += vi.adj();
                           });
}
 
}  // namespace math
}  // namespace stan
 
#endif