row_to_col_major_2d Subroutine

  subroutine row_to_col_major_2d(data_in, data_out, m, n)
    !! Convert flat row-major [m,n] to flat column-major [m,n]
    !! Inverse of col_to_row_major_2d.
    implicit none
    integer, intent(in) :: m, n
    real(real32), intent(in) :: data_in(m * n)
    real(real32), intent(out) :: data_out(m * n)
    integer :: i, j
    do i = 1, m
       do j = 1, n
          data_out((j-1)*m + i) = data_in((i-1)*n + j)
       end do
    end do
  end subroutine row_to_col_major_2d