The four stage method and a double gravity model were used to forecast the OD(origin-destination) distribution of air traffic flow in the whole airspace of China.
基于四阶段法，采用双重力模型，预测全国空域的交通流量OD分布。
Features of air traffic management and decision support system are introduced. Then, an improved four-stage standardized modeling method is proposed.
简单介绍了空中交通流量管理和决策支持系统的特点，对一种四阶段规范化数据建模方法加以改进。
From the primary school to the university, the methods of chinese study can be divided into four stages. The method of each stage is different, but has the common characteristic.
从小学到大学的语文学习可以划分为四个阶段，各阶段的教法、学法各异，但有以一贯之的共性，不存在不可逾越的鸿沟。
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