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# diet_cs.cs

    /* Copyright 2025, Gurobi Optimization, LLC */

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

    using System;
    using Gurobi;

    class diet_cs
    {
      static void Main()
      {
        try {

          // Nutrition guidelines, based on
          // USDA Dietary Guidelines for Americans, 2005
          // http://www.health.gov/DietaryGuidelines/dga2005/
          string[] Categories =
              new string[] { "calories", "protein", "fat", "sodium" };
          int nCategories = Categories.Length;
          double[] minNutrition = new double[] { 1800, 91, 0, 0 };
          double[] maxNutrition = new double[] { 2200, GRB.INFINITY, 65, 1779 };

          // Set of foods
          string[] Foods =
              new string[] { "hamburger", "chicken", "hot dog", "fries",
                  "macaroni", "pizza", "salad", "milk", "ice cream" };
          int nFoods = Foods.Length;
          double[] cost =
              new double[] { 2.49, 2.89, 1.50, 1.89, 2.09, 1.99, 2.49, 0.89,
                  1.59 };

          // Nutrition values for the foods
          double[,] nutritionValues = new double[,] {
              { 410, 24, 26, 730 },   // hamburger
              { 420, 32, 10, 1190 },  // chicken
              { 560, 20, 32, 1800 },  // hot dog
              { 380, 4, 19, 270 },    // fries
              { 320, 12, 10, 930 },   // macaroni
              { 320, 15, 12, 820 },   // pizza
              { 320, 31, 12, 1230 },  // salad
              { 100, 8, 2.5, 125 },   // milk
              { 330, 8, 10, 180 }     // ice cream
              };

          // Model
          GRBEnv env = new GRBEnv();
          GRBModel model = new GRBModel(env);

          model.ModelName = "diet";

          // Create decision variables for the nutrition information,
          // which we limit via bounds
          GRBVar[] nutrition = new GRBVar[nCategories];
          for (int i = 0; i < nCategories; ++i) {
            nutrition[i] =
                model.AddVar(minNutrition[i], maxNutrition[i], 0, GRB.CONTINUOUS,
                             Categories[i]);
          }

          // Create decision variables for the foods to buy
          //
          // Note: For each decision variable we add the objective coefficient
          //       with the creation of the variable.
          GRBVar[] buy = new GRBVar[nFoods];
          for (int j = 0; j < nFoods; ++j) {
            buy[j] =
                model.AddVar(0, GRB.INFINITY, cost[j], GRB.CONTINUOUS, Foods[j]);
          }

          // 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 (int i = 0; i < nCategories; ++i) {
            GRBLinExpr ntot = 0.0;
            for (int j = 0; j < nFoods; ++j)
              ntot.AddTerm(nutritionValues[j,i], buy[j]);
            model.AddConstr(ntot == nutrition[i], Categories[i]);
          }

          // Solve
          model.Optimize();
          PrintSolution(model, buy, nutrition);

          Console.WriteLine("\nAdding constraint: at most 6 servings of dairy");
          model.AddConstr(buy[7] + buy[8] <= 6.0, "limit_dairy");

          // Solve
          model.Optimize();
          PrintSolution(model, buy, nutrition);

          // Dispose of model and env
          model.Dispose();
          env.Dispose();

        } catch (GRBException e) {
          Console.WriteLine("Error code: " + e.ErrorCode + ". " +
              e.Message);
        }
      }

      private static void PrintSolution(GRBModel model, GRBVar[] buy,
                                        GRBVar[] nutrition) {
        if (model.Status == GRB.Status.OPTIMAL) {
          Console.WriteLine("\nCost: " + model.ObjVal);
          Console.WriteLine("\nBuy:");
          for (int j = 0; j < buy.Length; ++j) {
            if (buy[j].X > 0.0001) {
              Console.WriteLine(buy[j].VarName + " " + buy[j].X);
            }
          }
          Console.WriteLine("\nNutrition:");
          for (int i = 0; i < nutrition.Length; ++i) {
            Console.WriteLine(nutrition[i].VarName + " " + nutrition[i].X);
          }
        } else {
          Console.WriteLine("No solution");
        }
      }
    }

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