Question

我想使用列式建模解决cplex中的一个简单问题。这是问题，

maximize 2x + 3y
subject to   x<= 5
             y<=2
            x,y >=0

以下是我必须编写的代码来解决它：

public static void Model_1() {
        try {
            //create new model
            IloCplex cplex = new IloCplex();
            //define variables
            IloNumVar x;
            IloNumVar y;
            IloObjective objective;
            objective = cplex.addMaximize();
            IloRange cons01;
            IloRange cons02;
            cons01 = cplex.addRange(0, 5, "c1");
            cons02 = cplex.addRange(0, 2, "c1");
            IloColumn new_col = cplex.column(objective, 2);
            IloColumn new_col2 = cplex.column(objective,3);
            new_col = new_col.and(cplex.column(cons01,1));
            new_col2 = new_col2.and(cplex.column(cons02,1));
            x = cplex.numVar(new_col, 0, Double.MAX_VALUE);
            y = cplex.numVar(new_col, 0, Double.MAX_VALUE);
//solve model
            if (cplex.solve()) {
                System.out.println("obj = "+cplex.getObjValue());
                System.out.println("x   = "+cplex.getValue(x));
                System.out.println("y   = "+cplex.getValue(y));
}
            else {
                System.out.println("Model not solved");
            }
            cplex.end();
        }
        catch (IloException exc) {
            exc.printStackTrace();
        }
    }

但我没有得到正确的解决方案。我在编写代码时犯了什么错误吗？

Answer 1

尝试调试此类问题时，将模型导出为LP格式以确保正确生成它总是有用的。您可以在调用cplex.solve之前添加以下代码行：

cplex.exportModel("model.lp");

如果你这样做，model.lp的内容如下所示：

Maximize
 obj: 2 x1 + 2 x2
Subject To
 c1: x1 + x2 - Rgc1  = 0
 c1: - Rgc1  = 0
Bounds
 0 <= Rgc1 <= 5
 0 <= Rgc1 <= 2
End

这揭示了你在程序中犯的两个错别字。即，您应该替换：

cons02 = cplex.addRange(0, 2, "c1");

与

cons02 = cplex.addRange(0, 2, "c2");

而且，您应该替换：

y = cplex.numVar(new_col, 0, Double.MAX_VALUE);

与

y = cplex.numVar(new_col2, 0, Double.MAX_VALUE);

完成这两个更改后，model.lp看起来像：

Maximize
 obj: 2 x1 + 3 x2
Subject To
 c1: x1 - Rgc1  = 0
 c2: x2 - Rgc2  = 0
Bounds
 0 <= Rgc1 <= 5
 0 <= Rgc2 <= 2
End

并且，您从程序中获得以下输出：

obj = 16.0
x   = 5.0
y   = 2.0

使用Java在Cplex中进行列式建模

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