mdivide_right_tri.hpp

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#ifndef STAN_MATH_PRIM_FUN_MDIVIDE_RIGHT_TRI_HPP
#define STAN_MATH_PRIM_FUN_MDIVIDE_RIGHT_TRI_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 <Eigen::UpLoType TriView, typename EigMat1, typename EigMat2,
          require_all_eigen_t<EigMat1, EigMat2>* = nullptr>
inline auto mdivide_right_tri(const EigMat1& b, const EigMat2& A) {
  check_square("mdivide_right_tri", "A", A);
  check_multiplicable("mdivide_right_tri", "b", b, "A", A);
  if (TriView != Eigen::Lower && TriView != Eigen::Upper) {
    throw_domain_error("mdivide_right_tri",
                       "triangular view must be Eigen::Lower or Eigen::Upper",
                       "", "");
  }
  using T_return = return_type_t<EigMat1, EigMat2>;
  using ret_type = Eigen::Matrix<T_return, Eigen::Dynamic, Eigen::Dynamic>;
  if (A.rows() == 0) {
    return ret_type(b.rows(), 0);
  }
 
  return ret_type(A)
      .template triangularView<TriView>()
      .transpose()
      .solve(ret_type(b).transpose())
      .transpose()
      .eval();
}
 
}  // namespace math
}  // namespace stan
 
#endif