3.3 Define Sustainable Development and Unsustainab...
It is quite difficult to directly determine a reasonable boundary between sustainable development and unsustainable development.According to our model,the evaluation values of Driving forces,Pressures,States,Impacts,Responses for each stage,as well as the ODEs of their factors,can be obtained.We select 10 countries in the world acknowledged as the most sustainable development and 10 countries,the least sustainable development,and use the model to calculate the values of each indicator.Then we can define the boundary between sustainable development and unsustainable development according to the data difference between the least sustainable country and the most sustainable country.
•Determine the boundary between sustainable development and unsustainable development from the state macro-perspective
The figure shows that the average Pressure P best of the least sustainable country is significantly higher than that of the most sustainable one,while the average State S best of the most sustainable country is significantly lower than that of the least sustainable one.So we can conclude that a country with low Pressure and high State is sustainable while a country with high Pressure and low State is unsustainable.Accordingly we define the sustainability of a country as follows：
Of which 
respectively represent the medium level of sustainability Pressure and State andα the contribution of Pressure and State to the sustainability.The value of needs to be further discussed.We first suppose
,that is to say,
•Determine the boundary between sustainable development and unsustainable development of indicators
The 10 countries in the world acknowledged as the most sustainable development and the 10 countries,the least sustainable development are shown in Table 3,Table 4.
Table 3 The 10 countries of the most sustainable development
Table 4 The 10 countries of the list sustainable development
Supposing the ith value of indicator is Fi,we get the average level Fi max and F i min respectively represent for the most sustainable country and the least sustainable country.We define the contribution indicator of a certain field to the sustainability as follows：
Of which
is the boundary value of the indicator between sustainable development and unsustainable development,andγi refers to the importance of the indicator.The contribution indicator is as follows：
