trace_quad_form.hpp

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#ifndef STAN_MATH_PRIM_FUN_TRACE_QUAD_FORM_HPP
#define STAN_MATH_PRIM_FUN_TRACE_QUAD_FORM_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/fun/to_ref.hpp>
 
namespace stan {
namespace math {
 
template <typename EigMat1, typename EigMat2,
          require_all_eigen_vt<std::is_arithmetic, EigMat1, EigMat2>* = nullptr>
inline return_type_t<EigMat1, EigMat2> trace_quad_form(const EigMat1& A,
                                                       const EigMat2& B) {
  check_square("trace_quad_form", "A", A);
  check_multiplicable("trace_quad_form", "A", A, "B", B);
  const auto& B_ref = to_ref(B);
  return B_ref.cwiseProduct(A * B_ref).sum();
}
 
}  // namespace math
}  // namespace stan
 
#endif