mdivide_left.hpp

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#ifndef STAN_MATH_PRIM_FUN_MDIVIDE_LEFT_HPP
#define STAN_MATH_PRIM_FUN_MDIVIDE_LEFT_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/Eigen.hpp>
 
namespace stan {
namespace math {
 
template <typename T1, typename T2,
          require_all_eigen_vt<std::is_arithmetic, T1, T2>* = nullptr>
inline Eigen::Matrix<return_type_t<T1, T2>, T1::RowsAtCompileTime,
                     T2::ColsAtCompileTime>
mdivide_left(const T1& A, const T2& b) {
  check_square("mdivide_left", "A", A);
  check_multiplicable("mdivide_left", "A", A, "b", b);
  if (A.size() == 0) {
    return {0, b.cols()};
  }
 
  return Eigen::Matrix<return_type_t<T1, T2>, T1::RowsAtCompileTime,
                       T1::ColsAtCompileTime>(A)
      .lu()
      .solve(Eigen::Matrix<return_type_t<T1, T2>, T2::RowsAtCompileTime,
                           T2::ColsAtCompileTime>(b));
}
 
}  // namespace math
}  // namespace stan
 
#endif