mip2_vb.vb
' Copyright 2019, Gurobi Optimization, LLC ' ' This example reads a MIP model from a file, solves it and ' prints the objective values from all feasible solutions ' generated while solving the MIP. Then it creates the fixed ' model and solves that model. Imports System Imports Gurobi Class mip2_vb Shared Sub Main(ByVal args As String()) If args.Length < 1 Then Console.WriteLine("Usage: mip2_vb filename") Return End If Try Dim env As GRBEnv = New GRBEnv("lp1.log") Dim model As GRBModel = New GRBModel(env, args(0)) If model.IsMIP = 0 Then Console.WriteLine("Model is not a MIP") Return End If model.Optimize() Dim optimstatus As Integer = model.Status If optimstatus = GRB.Status.INF_OR_UNBD Then model.Parameters.Presolve = 0 model.Optimize() optimstatus = model.Status End If Dim objval As Double If optimstatus = GRB.Status.OPTIMAL Then objval = model.ObjVal Console.WriteLine("Optimal objective: " & objval) ElseIf optimstatus = GRB.Status.INFEASIBLE Then Console.WriteLine("Model is infeasible") model.ComputeIIS() model.Write("model.ilp") Return ElseIf optimstatus = GRB.Status.UNBOUNDED Then Console.WriteLine("Model is unbounded") Return Else Console.WriteLine("Optimization was stopped with status = " & _ optimstatus) Return End If ' Iterate over the solutions and compute the objectives Dim vars() As GRBVar = model.GetVars() model.Parameters.OutputFlag = 0 Console.WriteLine() For k As Integer = 0 To model.SolCount - 1 model.Parameters.SolutionNumber = k Dim objn As Double = 0.0 For j As Integer = 0 To vars.Length - 1 objn += vars(j).Obj * vars(j).Xn Next Console.WriteLine("Solution " & k & " has objective: " & objn) Next Console.WriteLine() model.Parameters.OutputFlag = 1 ' Solve fixed model Dim fixedmodel As GRBModel = model.FixedModel() fixedmodel.Parameters.Presolve = 0 fixedmodel.Optimize() Dim foptimstatus As Integer = fixedmodel.Status If foptimstatus <> GRB.Status.OPTIMAL Then Console.WriteLine("Error: fixed model isn't optimal") Return End If Dim fobjval As Double = fixedmodel.ObjVal If Math.Abs(fobjval - objval) > 0.000001 * (1.0 + Math.Abs(objval)) Then End If Dim fvars() As GRBVar = fixedmodel.GetVars() Dim x() As Double = fixedmodel.Get(GRB.DoubleAttr.X, fvars) Dim vnames() As String = fixedmodel.Get(GRB.StringAttr.VarName, fvars) For j As Integer = 0 To fvars.Length - 1 If x(j) <> 0 Then Console.WriteLine(vnames(j) & " " & x(j)) End If Next ' Dispose of models and env fixedmodel.Dispose() model.Dispose() env.Dispose() Catch e As GRBException Console.WriteLine("Error code: " & e.ErrorCode & ". " & e.Message) End Try End Sub End Class
