Assume that the basic variable is commodity, z is total profit, and the selling price of the basic variable is value coefficient Cj, that is, unit price.
According to the test number formula
It can be understood vividly as follows: if Cj is greater than z, that is, the basic variable is sold, then it means that the single product with Cj as the selling value coefficient is greater than the total profit of selling the basic variable (that is, the number of tests is greater than zero), then the goods sold will actually have greater profits, which can make the objective function z continue to increase.
If all the test coefficients are less than or equal to 0, it proves that it is impossible to increase the profit (z) by changing the sales of any other commodity (variable).