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mip2_vb.vb
' Copyright 2020, 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
