鞍点（Saddle point）在微分方程中，沿着某一方向是稳定的，另一条方向是不稳定的奇点，叫做鞍点。在泛函中，既不是极大值点也不是极小值点的临界点，叫做鞍点。-The saddle point (point Saddle) in the differential equation, along a certain direction is stable, and the other direction is not stable singular point, called the s