std::linalg::multipliable

namespace std::linalg {
  constexpr bool multipliable(
    const in-matrix auto& in_mat,
    const in-vector auto& in_vec,
    const in-vector auto& out_vec)
  {
    return out_vec.extent(0) == in_mat.extent(0) &&
           in_mat.extent(1) == in_vec.extent(0);
  } // (1)

  constexpr bool multipliable(
    const in-vector auto& in_vec,
    const in-matrix auto& in_mat,
    const in-vector auto& out_vec)
  {
    return out_vec.extent(0) == in_mat.extent(1) &&
           in_mat.extent(0) == in_vec.extent(0);
  } // (2)

  constexpr bool multipliable(
    const in-matrix auto& in_mat1,
    const in-matrix auto& in_mat2,
    const in-matrix auto& out_mat)
  {
    return out_mat.extent(0) == in_mat1.extent(0) &&
           out_mat.extent(1) == in_mat2.extent(1) &&
           in1_mat.extent(1) == in_mat2.extent(0);
  } // (3)
}