The variable sex ratio of sea lampreys will affect the interaction between the populations in the ecosystem. This paper establishes a statistical model of the change of sea lampreys’ sex ratio and a differential equation model of various population interactions to describe this effect, and analyzes it based on Lyapunov's qualitative theory. Based on an example in the Great Lakes region of North America, we verify the proposed mathematical model and analyze its sensitivity. The results showed that the sex ratio of the population can be increased by reducing the available resources of young lampreys, and it is feasible to control the number of lampreys in this way. Qualitative theory shows that the differential equation model has no stable equilibrium point, reflecting that the numbers of various populations will change dynamically when the sex ratio of lampreys changes. The mathematical model established by us also has good stability.
The 17 Sustainable Development Goals (SDGs) proposed by the UN are not independent of each other. In this article, we analyze the reciprocal influence of 17 SDGs, on the basis of which we propose Network-based Priority Selection Algorithm (NPSA), in which static and dynamic networks are constructed. The static network is established to describe the fundamental interaction between 17 SDGs by using Cross-impact Matrix for Targets. Fiscal expenditure, main driving force of the development of 17 SDGs, is mainly invested in ten fields. So we set up a Field-Goal Map by counting the number of targets they include in common. Then we establish four priority selection indicators, including centrality, system impact, urgency and development-based modification. According to the various developing level of different countries, we assign personalized weight vectors for them to synthesize the influence of the four indicators using the Entropy Weight Method. Then we get priority score of each goal and its rank for each year. We quantitatively simulate system dynamics to implement scenario analysis on a ten-year horizon. Once a year, we re-rank the priority of 17 SDGs and then use conservative, steady, or aggressive strategies to allocate financial expenditure. Considering the delay effect between investment and reward, we propose Delay-based Breadth-First Search Algorithm (D-BFS) to update our network, broadcasting the influence of one goal to another once a month. Logistic curve in is used to simulate the S-shaped curve change of the degree of mutual influence between goals. We use the dynamic model to give guidance on financial investment for each goal in the next ten years. Moreover, facing global field mutation and crisis, the development strategy calculated by our model has excellent stability. The code is released at https://github.com/GoodMorningPeter/NPSA.
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