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callback_vb.vb
' Copyright 2023, Gurobi Optimization, LLC
' This example reads a model from a file, sets up a callback that
' monitors optimization progress and implements a custom
' termination strategy, and outputs progress information to the
' screen and to a log file.
'
' The termination strategy implemented in this callback stops the
' optimization of a MIP model once at least one of the following two
' conditions have been satisfied:
' 1) The optimality gap is less than 10%
' 2) At least 10000 nodes have been explored, and an integer feasible
' solution has been found.
' Note that termination is normally handled through Gurobi parameters
' (MIPGap, NodeLimit, etc.). You should only use a callback for
' termination if the available parameters don't capture your desired
' termination criterion.
Imports System
Imports Gurobi
Class callback_vb
Inherits GRBCallback
Private vars As GRBVar()
Private lastnode As Double
Private lastiter As Double
Public Sub New(ByVal xvars As GRBVar())
vars = xvars
lastnode = lastiter = -1
End Sub
Protected Overloads Overrides Sub Callback()
Try
If where = GRB.Callback.PRESOLVE Then
' Presolve callback
Dim cdels As Integer = GetIntInfo(GRB.Callback.PRE_COLDEL)
Dim rdels As Integer = GetIntInfo(GRB.Callback.PRE_ROWDEL)
Console.WriteLine(cdels & " columns and " & rdels & " rows are removed")
ElseIf where = GRB.Callback.SIMPLEX Then
' Simplex callback
Dim itcnt As Double = GetDoubleInfo(GRB.Callback.SPX_ITRCNT)
If itcnt Mod - lastiter >= 100 Then
lastiter = itcnt
Dim obj As Double = GetDoubleInfo(GRB.Callback.SPX_OBJVAL)
Dim pinf As Double = GetDoubleInfo(GRB.Callback.SPX_PRIMINF)
Dim dinf As Double = GetDoubleInfo(GRB.Callback.SPX_DUALINF)
Dim ispert As Integer = GetIntInfo(GRB.Callback.SPX_ISPERT)
Dim ch As Char
If ispert = 0 Then
ch = " "c
ElseIf ispert = 1 Then
ch = "S"c
Else
ch = "P"c
End If
Console.WriteLine(itcnt & " " & obj & ch & " " & pinf & " " & dinf)
End If
ElseIf where = GRB.Callback.MIP Then
' General MIP callback
Dim nodecnt As Double = GetDoubleInfo(GRB.Callback.MIP_NODCNT)
If nodecnt - lastnode >= 100 Then
lastnode = nodecnt
Dim objbst As Double = GetDoubleInfo(GRB.Callback.MIP_OBJBST)
Dim objbnd As Double = GetDoubleInfo(GRB.Callback.MIP_OBJBND)
If Math.Abs(objbst - objbnd) < 0.1 * (1.0R + Math.Abs(objbst)) Then
Abort()
End If
Dim actnodes As Integer = CInt(GetDoubleInfo(GRB.Callback.MIP_NODLFT))
Dim itcnt As Integer = CInt(GetDoubleInfo(GRB.Callback.MIP_ITRCNT))
Dim solcnt As Integer = GetIntInfo(GRB.Callback.MIP_SOLCNT)
Dim cutcnt As Integer = GetIntInfo(GRB.Callback.MIP_CUTCNT)
Console.WriteLine(nodecnt & " " & actnodes & " " & itcnt & " " & _
objbst & " " & objbnd & " " & solcnt & " " & cutcnt)
End If
ElseIf where = GRB.Callback.MIPSOL Then
' MIP solution callback
Dim obj As Double = GetDoubleInfo(GRB.Callback.MIPSOL_OBJ)
Dim nodecnt As Integer = CInt(GetDoubleInfo(GRB.Callback.MIPSOL_NODCNT))
Dim x As Double() = GetSolution(vars)
Console.WriteLine("**** New solution at node " & nodecnt & ", obj " & _
obj & ", x(0) = " & x(0) & "****")
End If
Catch e As GRBException
Console.WriteLine("Error code: " & e.ErrorCode & ". " & e.Message)
Console.WriteLine(e.StackTrace)
End Try
End Sub
Shared Sub Main(ByVal args As String())
If args.Length < 1 Then
Console.WriteLine("Usage: callback_vb filename")
Return
End If
Try
Dim env As New GRBEnv()
Dim model As New GRBModel(env, args(0))
Dim vars As GRBVar() = model.GetVars()
' Create a callback object and associate it with the model
model.SetCallback(New callback_vb(vars))
model.Optimize()
Dim x As Double() = model.Get(GRB.DoubleAttr.X, vars)
Dim vnames As String() = model.Get(GRB.StringAttr.VarName, vars)
For j As Integer = 0 To vars.Length - 1
If x(j) <> 0.0R Then
Console.WriteLine(vnames(j) & " " & x(j))
End If
Next
' Dispose of model and env
model.Dispose()
env.Dispose()
Catch e As GRBException
Console.WriteLine("Error code: " & e.ErrorCode & ". " & e.Message)
Console.WriteLine(e.StackTrace)
End Try
End Sub
End Class
