One is the saddle-type structure where the projection point is located either in the up part or the down part of the phase plane, which is divided by both stable and unstable manifolds.

一类是投影点处的轨迹走向服从鞍点规律，且由于投影点位于稳定流形与不稳定流形分割的相平面的上部或下部，故轨迹将沿稳定流形方向到达动态鞍点再沿不稳定流形方向离开该点；

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