一、前言在化学工程和石油炼制的工艺设计中,常常遇到这种情况:所建立的数学模型中,变量数 M 多于方程式数 N,即M-N=FF 称为自由度。也就是说,要解方程组,设计者必须从变量中选出 F 个变量并赋予一定的符合情理的数值,使未知变量数与方程式数相等,才能使方程组得解。所以又称为设计变量。如果选择的为最优设计变量则方程组可以很顺利的解出。当前选择最优设计变量的方法均采用双层图法(Bipartite graph method),但这种方法又要画图又要联线,十分繁 I. Introduction In chemical engineering and oil refining process design, often encountered such a situation: the mathematical model established, the number of variables M is more than the number of equations N, that M-N = FF is called the degree of freedom. That is to say, to solve a system of equations, the designer must select F variables from the variables and assign some reasonable values ​​so that the equations are solved if the unknown variables are equal to the number of equations. So it is also called design variable. If you choose the optimal design variables, the equations can be solved very smoothly. Currently, the methods for selecting the optimal design variables are all based on the Bipartite graph method. However, this method has to be drawn and connected, which is very complicated