Pedagogical dialogue is not only a kind of pedagogical method, relationship and recognitive style but a spirit.
教学对话不单是一种教学方法、教学关系和教学认知方式，而是一种教学精神。
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It also builds systematic dynamics model to illustrate the relationship and function of key factors in recognitive process by analysis on the organization learning process.
In this paper, the method for the optimal gray threshold is given, which is based on the maximum class separation distance criterion of pattern recognitive decision theory.