indexing section造句

First , we simply introduced the optical wave - guide theory : the fluctuation equations of planar wave - guide and the preparation of embranchment wave - guide . then based on maxwell equations and in the paraxial limit we deduced the formula needed in calculating fd - bpm . the refractive index section was n ( x , y )
然后我们在maxwell方程的基础上，根据慢包络近似理论，在折射率截面为n ( x ， z )的条件下，利用有限差分近似来代替偏微分方程，推出了有限差分光束传播法计算所需要的公式。
It's difficult to find indexing section in a sentence. 用indexing section造句挺难的