According to the present situation and development of water environment, fuzzy mathematics comprehensive evaluation method is adopted to establish evaluation factor set and comment set, determine weight vector, combine factor evaluation matrix, determine membership degree, objectively evaluate river water quality, and take the grade corresponding to the maximum membership degree as the river water quality grade.

Keywords: fuzzy comprehensive evaluation factor membership evaluation matrix

This topic only uses some water pollution factors to represent the overall evaluation of river water.

The data contents of the river to be measured are 79, 7.04, 4.92 and 0.5 1, with units of. Try to determine which grade the water quality of this river belongs to.

According to relevant regulations, the water quality grading standards are shown in the following table:

Water quality classification standard table (mg/L)

ⅰⅱⅲⅳⅴ

SS 50 150 250 350 350

Do 7.5 6 5 3 2

cod Mn 2 4 6 8 10

NH3-N 0. 15 0.5 1. 1.5 2

1. Establish an evaluation object factor number set and a water quality grade evaluation set. Comparing the measured data with the grading standards, only the first four grades are selected for judgment, and a matrix is obtained:

Appraisal object

2. Standardize the data. Here, the ratio of a single population is used to standardize the evaluation set A: a standardized matrix is obtained.

B is standardized in this way

3. Calculation of intimacy. The proximity of matrix D to a column of matrix C indicates the proximity of samples to a certain level, and the high level can be approximately classified as this level. Here, the relative distance closeness is adopted: from this, the closeness matrix can be obtained:

4. Calculation of weight vector. In water environment assessment, the number of pollution factors is increasing, and the importance of a single factor to water environment is different. Determining the weight of a single factor has a great influence on the final evaluation result. Considering that different pollution factors have different contribution rates to the river pollution degree, the same pollution factor may have different contribution rates to the pollution degree under different grades, so the contribution rates of pollution factors under different grades are calculated here. According to the standardized matrix c obtained before, the weights of different pollution factors under J level are determined, so as to obtain the weight vector set.

5. Calculation of final membership: The water quality of a river belongs to Grade J, which can be calculated. When the maximum value is taken, the corresponding grade is the grade to which the river belongs, = 0.849225.

Therefore, the water quality of the river belongs to the second category. The river water quality is in good condition.