| Energy is an important material basis for a country's economic development; meanwhile coal is the foundation energy in China. As an important strategic resource, coal plays a very important role in our country's economic construction and in realizing an all-round well-off society. Energy security not only concerns a country's economic security, but also affects the social and political stability.China is one of the largest coal producing and consuming countries. Coal industry is our country's foundation industry. Because of the fact that China has abundant coal reserves, poor petroleum and gas reserves, and China's economic and technology development level is relatively backward, China's energy supply pattern which takes coal as a leading will not change in future for a long time, although as energy structure is adjusted, the demand and dependence on petroleum are becoming more and more.China coal industry has experienced rapid growth in the last several years, and coal production and demand have been continuously increasing. After the rapid growth of the total profit in coal industry from 2003-2005, and as macro-control measures are implemented, now our country's coal market are changing from over-demand to smooth transition period, and the increasing speed of coal demand is gradually becoming slow. The national coal production was 2.38 billion in 2006, which was 0.18 billion more than 2005, and the increasing speed was 8%. In 2007 the raw coal production was 2.5 billion, and the increasing speed was 9.35%. About 60% of China's coal resources is existing in the "three west" area-Shanxi, Shanxi and Inner Mongolia West, while the main consumption concentrates in eastern coastal area which is the economic developed area in China. So this characteristic that coal consumption and resources distribution are not consistent has determined our country's basic transportation pattern-north-south coal transmission and west-east coal transmission. During the "11th five-year plan" period, China is still in the period of rapid development of industrialization and urbanization. Energy consumption and coal demand will continuously increase.The coal supply and demand are so important to national economic that many scholars domestic and foreign have thorough research on it. However most of these studies were based on the fixed parameter model and most researches are about long run elastic study and prediction. As the further development of the market economy reform and the continuous change of the economic structure, the extent that the factors affect the coal supply and demand has been also changing continuously. Therefore the fixed model already can not describe the extent exactly. However the time varying parameter model this paper used can reflect the real economic operation.State space model studies the relationship between the parameter that can be observed and inner system state, so we can make an analysis and observation through estimating various state parameters. State space model can be usually estimated by kalman filter, because kalman filter can not only be used to estimate likelihood function, but predict and smooth the state parameter that can not be observed. When a model is expressed in state space model, we can use kalman filter to solve it. Kalman filter is the most ideal recursive process for calculating state vector based on all the information that can be obtained. The main function of kalman filter is when the disturbing term and initial state vector obey normal distribution; it can calculate likelihood function through predicting error decomposition. Therefore we can estimate all the unknown parameters, and when we get the new observation, we can use kalman filter to correct the estimation of state vector.This paper analyzed and selected the factors that affect supply-demand of our country's coal industry, and constructed a time varying parameter model using the state space model and kalman filter:(l)Supply Function Model Where ymsa represents raw coal production after season-adjustment, gzsa and lzsa respectively represent the average balance of net value of fixed assets and the monthly average balance of circulating funds after season-adjustment. And svl is the sensitive degree of each point in time which coal production affected by the average balance of net value of fixed assets, namely elasticity. sv2 is the sensitive degree of each point in time which coal production affected by the average balance of net value of current assets.(2)Demand Function Modelwhere rxssrsa represents the real sales revenue after season-adjustment, and gdpsa, bzsa, cbsa respectively represent national income, the proportion of heavy industry value-added in industry value-added, transportation cost after season-adjustment.shl represents the sensitive degree of each point in time which sales revenue affected by transportation cost, namely elasticity, and shl is the time varying sequence. After the analysis of the results, we can get the conclusions as follows:(1) Among the factors that affect the coal supply, the capital construction investment in the coal industry, fixed assets and current assets etc., have some contribution to the coal production. The volatility of the contribution of fixed assets is relatively larger. After several years' smooth change, the contribution has the trend to rise in the last two years. But from the long run trend, we can see that it will not change greatly. Therefore only add fixed assets investment can not make the coal production increase greatly. The elasticity of the coal production with respect to the current assets has the tendency to rise, which reflects that the current assets slightly increase its impact on the production. Hence, Keeping a high current assets in the future will have a large contribution to the coal production. However as an input, the labor has no significant effect on the coal production.(2)The factors that affect the coal demand contains national income, the proportion of heavy industry and transportation cost. The national income and the proportion of heavy industry have positive and great impact on the change of coal demand. So as the national income increases, the coal demand will continuously increase in future. As the adjustment of industrial structure, the change of the proportion of heavy industry will also have great impact on the coal demand. The change of the transportation cost has a negative and great effect on the coal demand, with the elasticity more than 1. In future, with the improvement of the railway situation, the cost is hopeful to be lower, and thereupon the coal demand will increase. The change of the coal price has no significant effect on coal demand, and the change of coal demand is the main reason for the change of the coal price. |
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