Who can explain the following questions about transfer matrix? formula (31) in New Journal of Physics, Vol.12 123020. [http://iopscience.iop.org/1367-2630/12/12/123020/pdf/1367-2630_12_12_123020.pdf] is different from the result of another paper in Journal of Physics:Condensed matter (Vol.21, 045305 (2009))[http://iopscience.iop.org/0953-8984/21/4/045305/pdf/0953-8984_21_4_045305.pdf]. The expression for transfer matrix is different from each other, even if for a single trench. Who can give me a hint or instruction?