Try our new documentation site.


lpmod_vb.vb


' Copyright 2023, Gurobi Optimization, LLC
'
' This example reads an LP model from a file and solves it.
' If the model can be solved, then it finds the smallest positive variable,
' sets its upper bound to zero, and resolves the model two ways:
' first with an advanced start, then without an advanced start
' (i.e. from scratch).

Imports System
Imports Gurobi

Class lpmod_vb
    Shared Sub Main(ByVal args As String())

        If args.Length < 1 Then
            Console.WriteLine("Usage: lpmod_vb filename")
            Return
        End If

        Try
            ' Read model and determine whether it is an LP
            Dim env As New GRBEnv()
            Dim model As New GRBModel(env, args(0))
            If model.IsMIP <> 0 Then
                Console.WriteLine("The model is not a linear program")
                Environment.Exit(1)
            End If

            model.Optimize()

            Dim status As Integer = model.Status

            If (status = GRB.Status.INF_OR_UNBD) OrElse _
               (status = GRB.Status.INFEASIBLE) OrElse _
               (status = GRB.Status.UNBOUNDED) Then
                Console.WriteLine("The model cannot be solved because it is " & _
                                  "infeasible or unbounded")
                Environment.Exit(1)
            End If

            If status <> GRB.Status.OPTIMAL Then
                Console.WriteLine("Optimization was stopped with status " & status)
                Environment.Exit(0)
            End If

            ' Find the smallest variable value
            Dim minVal As Double = GRB.INFINITY
            Dim minVar As GRBVar = Nothing
            For Each v As GRBVar In model.GetVars()
                Dim sol As Double = v.X
                If (sol > 0.0001) AndAlso _
                   (sol < minVal) AndAlso _
                   (v.LB = 0.0) Then
                    minVal = sol
                    minVar = v
                End If
            Next

            Console.WriteLine(vbLf & "*** Setting " & _
                              minVar.VarName & " from " & minVal & " to zero ***" & vbLf)
            minVar.UB = 0

            ' Solve from this starting point
            model.Optimize()

            ' Save iteration & time info
            Dim warmCount As Double = model.IterCount
            Dim warmTime As Double = model.Runtime

            ' Reset the model and resolve
            Console.WriteLine(vbLf & "*** Resetting and solving " & _
                              "without an advanced start ***" & vbLf)
            model.Reset()
            model.Optimize()

            Dim coldCount As Double = model.IterCount
            Dim coldTime As Double = model.Runtime

            Console.WriteLine(vbLf & "*** Warm start: " & warmCount & _
                              " iterations, " & warmTime & " seconds")

            Console.WriteLine("*** Cold start: " & coldCount & " iterations, " & _
                              coldTime & " seconds")

            ' Dispose of model and env
            model.Dispose()
            env.Dispose()

        Catch e As GRBException
            Console.WriteLine("Error code: " & e.ErrorCode & ". " & e.Message)
        End Try
    End Sub
End Class

Try Gurobi for Free

Choose the evaluation license that fits you best, and start working with our Expert Team for technical guidance and support.

Evaluation License
Get a free, full-featured license of the Gurobi Optimizer to experience the performance, support, benchmarking and tuning services we provide as part of our product offering.
Academic License
Gurobi supports the teaching and use of optimization within academic institutions. We offer free, full-featured copies of Gurobi for use in class, and for research.
Cloud Trial

Request free trial hours, so you can see how quickly and easily a model can be solved on the cloud.

Search