tsp_vb.vb.
'版权所有2021，Gurobi O狗万app足彩ptimization，LLC'使用延迟约束在随机生成的“点”中解决旅行推销员问题。基础MIP模型仅包括“学位-2”约束，要求每个节点具有完全'两个事件边缘。对此模型的解决方案可能包含子台楼 - “不访问每个节点的旅行”。惰性约束回调'为关闭它们添加新约束。导入Gurobi类TSP_VB继承GRBCallback私有变量作为GRBVAR（，）公共子新子新建（XVAR为GRBVAR（，））vars = XVARS结束子子会消除回调。如果找到可行的解决方案，则“找到最小的子大厅，并在巡回赛不访问每个节点时添加子从消除约束”。受保护的覆盖子回调（）尝试= grb.callback.mipsol然后'找到整数可行解决方案 - 它是否访问每个节点？Dim n为Integer = vars.getLength（0）Dim Tour为Integer（）= findsubtour（getsolubtour（getsolud（vars））如果tour.length 0.5 AndAlso Not seen(i) node = i Exit For End If Next If i = n len = len + 1 If len < bestlen bestlen = len bestind = start End If start = start + len Exit For End If Next End While For i = 0 To bestlen - 1 tour(i) = tour(bestind+i) Next System.Array.Resize(tour, bestlen) Return tour End Function ' Euclidean distance between points 'i' and 'j' Protected Shared Function distance(x As Double(), y As Double(), _ i As Integer, j As Integer) As Double Dim dx As Double = x(i) - x(j) Dim dy As Double = y(i) - y(j) Return Math.Sqrt(dx * dx + dy * dy) End Function Public Shared Sub Main(args As String()) If args.Length < 1 Then Console.WriteLine("Usage: tsp_vb nnodes") Return End If Dim n As Integer = Convert.ToInt32(args(0)) Try Dim env As New GRBEnv() Dim model As New GRBModel(env) ' Must set LazyConstraints parameter when using lazy constraints model.Parameters.LazyConstraints = 1 Dim x As Double() = New Double(n - 1) {} Dim y As Double() = New Double(n - 1) {} Dim r As New Random() For i As Integer = 0 To n - 1 x(i) = r.NextDouble() y(i) = r.NextDouble() Next ' Create variables Dim vars As GRBVar(,) = New GRBVar(n - 1, n - 1) {} For i As Integer = 0 To n - 1 For j As Integer = 0 To i vars(i, j) = model.AddVar(0.0, 1.0, distance(x, y, i, j), _ GRB.BINARY, "x" & i & "_" & j) vars(j, i) = vars(i, j) Next Next ' Degree-2 constraints For i As Integer = 0 To n - 1 Dim expr As GRBLinExpr = 0 For j As Integer = 0 To n - 1 expr.AddTerm(1.0, vars(i, j)) Next model.AddConstr(expr = 2.0, "deg2_" & i) Next ' Forbid edge from node back to itself For i As Integer = 0 To n - 1 vars(i, i).UB = 0.0 Next model.SetCallback(New tsp_vb(vars)) model.Optimize() If model.SolCount > 0 Then Dim tour As Integer() = findsubtour(model.Get(GRB.DoubleAttr.X, vars)) Console.Write("Tour: ") For i As Integer = 0 To tour.Length - 1 Console.Write(tour(i) & " ") Next Console.WriteLine() End If ' Dispose of model and environment 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
