Drawing on 185 cities in the northeastern region of China, this paper improves the radiation model by incorporating the accessibility index to characterize the asymmetric process of economic linkages before HSR in 2007 and after HSR in 2016. Then social network analysis is utilized to examine the impact of HSR on the spatial structure of economic networks, including nodal centrality and community structures. Finally, spatial econometric models are employed to explore the driving factors of nodal centrality in economic networks and some policy implications are proposed. The major findings of this paper are the following. First, HSR services can weaken the core-peripheral inequality of economic linkages and a corridor economy is evident in northeastern China. Second, HSR services have significantly improved the out-degree centrality of prefecture-level cities but have slightly decreased the in-degree centrality of Liaoning. Third, there was a slight decline of coherence in the economic network after the construction of HSR and the within-modular connections were strengthened by HSR. Four, the spatial error model (SEM) is more desirable for explaining the distribution of in-degree centrality. GDP, fixed asset investment, education, population, and fiscal expenditure are important contributors to the in-degree centrality in economic networks. These findings give significant insights into city system planning, integrated transport and land use development, formulating regional poles and the coordinated development across administrative boundaries in northeastern China.

To improve the ability for solving complex problems, an improved ant colony optimization algorithm with negative feedback strategy was proposed. Based on an inspired matrix, the new negative feedback strategy was designed to change the basic ant colony algorithm pheromone matrix to the opposite damper matrix. That was, even more dampers occurred on the shorter path found by the colony, reducing the probability that each section on the path was selected in the next time. Because of the enlightening matrix, the probability of more short circuit segments on the path was still greater in the process of optimization again, while the probability of longer path selected was decreased which was not easy to be selected in the next process. It was suitable to do further optimize. Through the experiment of TSP, it showed that the ant colony algorithm with combining the damper matrix and the original pheromone matrix can improve the searching ability obviously.