基本原理 假定初始点P0 ∈G0，沿某方 向(假定为X轴）前进△X时，到 达G+或G-(假定为G-)中的P1,在 沿另外一方向(Y轴)前进△Y,到 达P2。若P2 ∈G+，则改变前进 方向，否则继续向G+前进。-Basic Principle:

First ,initial point Pzero,assumed that Pzero belong to Gzero,moves the distance deltaX along one direction,assuming X axes,and reaches the point Pone belonging to Gplus or Gminus,assumed that it is Gminus.Then,it moves the distance deltaY along another direction ,that is Y axes,and reaches the point Ptwo.It will change the directon of moving if Ptwo belongs to Gplus or it will keep moving to Gplus.