Tempor al Var iations in Par ameter s of Gr avity Model: an Analysis on China''s Inter - city Railway Passenger Flows
重力模型系数时间变化路径分析 ———以中国城际铁路旅客交流为例

Gravity models are the basic tools which are widely applied in the research of spatial interaction(SI).It is well known that SI decreases as the distance increases or the mass decreases.The measurement and explanation on parameters are hot topics but the temporal variations of them are not discussed so frequently.This paper deals with how and why the parameters change with time by using the unrestrained gravity model and the data set consists of China's railway passenger flows between about 200 cities.We find that scale parameters show an increasing trend with a little fluctuation and distance-decay parameters grow over time instead of monotonic decrease over time.And an empirical and theoretical explanation will be given to why the general assumptions of monotonic increasing scale parameters and monotonic decreasing distance-decay parameters are not obeyed.