d4_dgemv321 Subroutine

subroutine d4_dgemv321(amat, xvec, yvec, alpha, beta, trans)
   real(dp), intent(in), contiguous, target :: amat(:, :, :)
   real(dp), intent(in), contiguous, target :: xvec(:, :)
   real(dp), intent(inout) :: yvec(:)
   real(dp), intent(in), optional :: alpha
   real(dp), intent(in), optional :: beta
   character(len=1), intent(in), optional :: trans
   real(dp), pointer :: aptr(:, :), xptr(:)
   character(len=1) :: tra
   if (present(trans)) then
      tra = trans
   else
      tra = 'n'
   end if
   if (any(tra == ['n', 'N'])) then
      aptr(1:size(amat, 1), 1:size(amat, 2)*size(amat, 3)) => amat
      xptr(1:size(xvec, 1)*size(xvec, 2)) => xvec
   else
      aptr(1:size(amat, 1)*size(amat, 2), 1:size(amat, 3)) => amat
      xptr(1:size(xvec, 1) * size(xvec, 2)) => xvec
   end if
   call d4_gemv(aptr, xptr, yvec, alpha, beta, tra)
end subroutine d4_dgemv321