This method was changed from measuring the dimension difference to the time difference measurement by using an optical system and circuitry.
这种方法利用一光学系统和电路，把线值差转换为时间差来测量。
The concept of extended boundary node was presented. By using finite difference method, the solution of the gained difference equations was given and simulated by computer.
由此提出了扩展边界节点的概念，并使用有限差分法，对所得到的差分方程组进行了计算机求解及模拟。
The time difference equation derived from unsaturated flow equation can be approximated by Galerkin finite element or finite difference method for space coordinate derivatives.
所得的非饱和土壤水运动方程对时间的差分方程，在空间上不仅可用有限元法而且可用有限差分法处理。
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