According to the theory of grey system

the grey cluster evaluation model of lake eutrophication was established by ① arranging the data into the sample matrix; ② determining the polarity of these data; ③ creating functions of weighted etiolation for each classification of the data and ④ producing the classification limits and weighted data for the lakes. Consequently

the overall weighted coefficient matrix

the triangle coordinates and the classifications

scores and ranks of the evaluated samples were achieved. This model was applied in evaluating the eutrophication of the 18 major lakes in China.