The Parabolic Equation method (PE) is an approximation of the wave equation, which models energy propagating in a cone centred on a preferred direction, the paraxial direction.
抛物线方程（PE）是波动方程的一种近似形式，它假设电磁波能量在沿着抛物线轴向的锥形区域内传播。
2
The paper gives a brief introduction to three types of mandrels used for the two-high pilger cold-rolling mill, namely, mono-cone mandrel, dual-cone mandrel and parabolic mandrel.