Try our new documentation site (beta).


diet_vb.vb


' Copyright 2024, Gurobi Optimization, LLC

' Solve the classic diet model, showing how to add constraints
' to an existing model.

Imports System
Imports Gurobi

Class diet_vb
    Shared Sub Main()
        Try

            ' Nutrition guidelines, based on
            ' USDA Dietary Guidelines for Americans, 2005
            ' http://www.health.gov/DietaryGuidelines/dga2005/
            Dim Categories As String() = New String() {"calories", "protein", "fat", _
                                                       "sodium"}
            Dim nCategories As Integer = Categories.Length
            Dim minNutrition As Double() = New Double() {1800, 91, 0, 0}
            Dim maxNutrition As Double() = New Double() {2200, GRB.INFINITY, 65, 1779}

            ' Set of foods
            Dim Foods As String() = New String() {"hamburger", "chicken", "hot dog", _
                                                  "fries", "macaroni", "pizza", _
                                                  "salad", "milk", "ice cream"}
            Dim nFoods As Integer = Foods.Length
            Dim cost As Double() = New Double() {2.49, 2.89, 1.5R, 1.89, 2.09, 1.99, _
                                                 2.49, 0.89, 1.59}

            ' Nutrition values for the foods
            ' hamburger
            ' chicken
            ' hot dog
            ' fries
            ' macaroni
            ' pizza
            ' salad
            ' milk
            ' ice cream
            Dim nutritionValues As Double(,) = New Double(,) {{410, 24, 26, 730}, _
                                                              {420, 32, 10, 1190}, _
                                                              {560, 20, 32, 1800}, _
                                                              {380, 4, 19, 270}, _
                                                              {320, 12, 10, 930}, _
                                                              {320, 15, 12, 820}, _
                                                              {320, 31, 12, 1230}, _
                                                              {100, 8, 2.5, 125}, _
                                                              {330, 8, 10, 180}}

            ' Model
            Dim env As New GRBEnv()
            Dim model As New GRBModel(env)

            model.ModelName = "diet"

            ' Create decision variables for the nutrition information,
            ' which we limit via bounds
            Dim nutrition As GRBVar() = New GRBVar(nCategories - 1) {}
            For i As Integer = 0 To nCategories - 1
                nutrition(i) = model.AddVar(minNutrition(i), maxNutrition(i), 0, _
                                            GRB.CONTINUOUS, Categories(i))
            Next

            ' Create decision variables for the foods to buy
            '
            ' Note: For each decision variable we add the objective coefficient
            '       with the creation of the variable.
            Dim buy As GRBVar() = New GRBVar(nFoods - 1) {}
            For j As Integer = 0 To nFoods - 1
                buy(j) = model.AddVar(0, GRB.INFINITY, cost(j), GRB.CONTINUOUS, _
                                      Foods(j))
            Next

            ' The objective is to minimize the costs
            '
            ' Note: The objective coefficients are set during the creation of
            '       the decision variables above.
            model.ModelSense = GRB.MINIMIZE

            ' Nutrition constraints
            For i As Integer = 0 To nCategories - 1
                Dim ntot As GRBLinExpr = 0
                For j As Integer = 0 To nFoods - 1
                    ntot.AddTerm(nutritionValues(j, i), buy(j))
                Next
                model.AddConstr(ntot = nutrition(i), Categories(i))
            Next

            ' Solve
            model.Optimize()
            PrintSolution(model, buy, nutrition)

            Console.WriteLine(vbLf & "Adding constraint: at most 6 servings of dairy")
            model.AddConstr(buy(7) + buy(8) <= 6, "limit_dairy")

            ' Solve
            model.Optimize()

            PrintSolution(model, buy, nutrition)

            ' 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

    Private Shared Sub PrintSolution(ByVal model As GRBModel, ByVal buy As GRBVar(), _
                                     ByVal nutrition As GRBVar())
        If model.Status = GRB.Status.OPTIMAL Then
            Console.WriteLine(vbLf & "Cost: " & model.ObjVal)
            Console.WriteLine(vbLf & "Buy:")
            For j As Integer = 0 To buy.Length - 1
                If buy(j).X > 0.0001 Then
                    Console.WriteLine(buy(j).VarName & " " & buy(j).X)
                End If
            Next
            Console.WriteLine(vbLf & "Nutrition:")
            For i As Integer = 0 To nutrition.Length - 1
                Console.WriteLine(nutrition(i).VarName & " " & nutrition(i).X)
            Next
        Else
            Console.WriteLine("No solution")
        End If
    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

Gurobi Optimization