#ifndef STAN_MATH_PRIM_MAT_FUN_MDIVIDE_LEFT_TRI_HPP
#define STAN_MATH_PRIM_MAT_FUN_MDIVIDE_LEFT_TRI_HPP

#include <boost/math/tools/promotion.hpp>
#include <stan/math/prim/mat/fun/Eigen.hpp>
#include <stan/math/prim/mat/fun/promote_common.hpp>
#include <stan/math/prim/mat/err/check_multiplicable.hpp>
#include <stan/math/prim/mat/err/check_square.hpp>

namespace stan {
  namespace math {

    /**
     * Returns the solution of the system Ax=b when A is triangular
     * @param A Triangular matrix.  Specify upper or lower with TriView
     * being Eigen::Upper or Eigen::Lower.
     * @param b Right hand side matrix or vector.
     * @return x = A^-1 b, solution of the linear system.
     * @throws std::domain_error if A is not square or the rows of b don't
     * match the size of A.
     */
    template <int TriView, typename T1, typename T2,
              int R1, int C1, int R2, int C2>
    inline
    Eigen::Matrix<typename boost::math::tools::promote_args<T1, T2>::type,
                  R1, C2>
    mdivide_left_tri(const Eigen::Matrix<T1, R1, C1> &A,
                     const Eigen::Matrix<T2, R2, C2> &b) {
      check_square("mdivide_left_tri", "A", A);
      check_multiplicable("mdivide_left_tri", "A", A, "b", b);
      return promote_common<Eigen::Matrix<T1, R1, C1>,
                            Eigen::Matrix<T2, R1, C1> >(A)
        .template triangularView<TriView>()
        .solve(promote_common<Eigen::Matrix<T1, R2, C2>,
               Eigen::Matrix<T2, R2, C2> >(b));
    }

    /**
     * Returns the solution of the system Ax=b when A is triangular and b=I.
     * @param A Triangular matrix.  Specify upper or lower with TriView
     * being Eigen::Upper or Eigen::Lower.
     * @return x = A^-1 .
     * @throws std::domain_error if A is not square
     */
    template<int TriView, typename T, int R1, int C1>
    inline
    Eigen::Matrix<T, R1, C1>
    mdivide_left_tri(const Eigen::Matrix<T, R1, C1> &A) {
      check_square("mdivide_left_tri", "A", A);
      int n = A.rows();
      Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic> b;
      b.setIdentity(n, n);
      A.template triangularView<TriView>().solveInPlace(b);
      return b;
    }

  }
}
#endif
