目标函数：min y 约束条件： y = 100, 0 <= x < 20 y = 60, 20 <= x < 30 y = 100, 30 <= x < 10800 x = 31 将这个模型用VB.NET调用Cplex求解

以下是用VB.NET调用Cplex求解上述模型的代码示例：

Imports ILOG.CPLEX
Imports System.IO

Module Module1
    Sub Main()
        Dim cplex As New Cplex()

        ' 创建变量 x 和 y
        Dim x As INumVar = cplex.NumVar(0, 10800, NumVarType.Float, "x")
        Dim y As INumVar = cplex.NumVar(0, 100, NumVarType.Float, "y")

        ' 创建约束条件
        Dim c1 As ILinearNumExpr = cplex.LinearNumExpr()
        c1.AddTerm(1.0, x)
        cplex.AddEq(c1, 31)

        Dim c2 As ILinearNumExpr = cplex.LinearNumExpr()
        c2.AddTerm(1.0, y)
        cplex.AddEq(c2, 100)

        Dim c3 As ILinearNumExpr = cplex.LinearNumExpr()
        c3.AddTerm(1.0, y)
        cplex.AddLe(c3, 60)

        Dim c4 As ILinearNumExpr = cplex.LinearNumExpr()
        c4.AddTerm(1.0, y)
        cplex.AddGe(c4, 100)

        Dim c5 As ILinearNumExpr = cplex.LinearNumExpr()
        c5.AddTerm(1.0, x)
        c5.AddTerm(-20.0, y)
        cplex.AddGe(c5, 0)

        Dim c6 As ILinearNumExpr = cplex.LinearNumExpr()
        c6.AddTerm(1.0, x)
        c6.AddTerm(-30.0, y)
        cplex.AddLe(c6, 0)

        ' 创建目标函数
        Dim obj As ILinearNumExpr = cplex.LinearNumExpr()
        obj.AddTerm(1.0, y)
        cplex.AddMinimize(obj)

        ' 求解优化模型
        If cplex.Solve() Then
            Console.WriteLine("Solution status = " + cplex.GetStatus().ToString())
            Console.WriteLine("Solution value  = " + cplex.ObjValue.ToString())

            Console.WriteLine("x = " + cplex.GetValue(x).ToString())
            Console.WriteLine("y = " + cplex.GetValue(y).ToString())
        Else
            Console.WriteLine("The problem is infeasible or unbounded.")
        End If

        cplex.End()
        Console.ReadKey()
    End Sub
End Module

请注意：在使用此代码之前，您需要先安装 CPLEX 和 IBM ILOG CPLEX Optimization Studio，并将其添加到您的 VB.NET 项目中。