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diet_vb.vb
' Copyright 2023, 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
