Evaluate LinearExp for the found solution

ortools/linear_solver/csharp/LinearExpr.cs

@@ -16,13 +16,18 @@
 using System;
 using System.Collections.Generic;
 
 public class LinearExpr
 {
     public virtual double DoVisit(Dictionary<Variable, double> coefficients, double multiplier)
     {
         return 0;
     }
 
+    public virtual double SolutionValue()
+    {
+        return 0;
+    }
+
     public double Visit(Dictionary<Variable, double> coefficients)
     {
         return DoVisit(coefficients, 1.0);
@@ -185,6 +190,11 @@
         }
     }
 
+    public override double SolutionValue()
+    {
+        return expr_.SolutionValue() * coeff_;
+    }
+
     private LinearExpr expr_;
     private double coeff_;
 }
@@ -213,6 +223,11 @@
             return 0.0;
         }
     }
+
+    public override double SolutionValue()
+    {
+        return expr_.SolutionValue() + coeff_;
+    }
 
     private LinearExpr expr_;
     private double coeff_;
@@ -246,6 +261,11 @@
         return 0.0;
     }
 
+    public override double SolutionValue()
+    {
+        return var_.SolutionValue();
+    }
+
     private Variable var_;
 }
 
@@ -274,6 +294,11 @@
         }
     }
 
+    public override double SolutionValue()
+    {
+        return left_.SolutionValue() + right_.SolutionValue();
+    }
+
     private LinearExpr left_;
     private LinearExpr right_;
 }
@@ -302,6 +327,16 @@
         }
     }
 
+    public override double SolutionValue()
+    {
+        double sum = 0.0;
+        foreach (LinearExpr expr in array_)
+        {
+            sum += expr.SolutionValue();
+        }
+        return sum;
+    }
+
     private LinearExpr[] array_;
 }
 
@@ -331,6 +366,16 @@
         return 0.0;
     }
 
+    public override double SolutionValue()
+    {
+        double sum = 0.0;
+        foreach (Variable var in array_)
+        {
+            sum += var.SolutionValue();
+        }
+        return sum;
+    }
+
     private Variable[] array_;
 }
 } // namespace Google.OrTools.LinearSolver

ortools/linear_solver/csharp/LinearSolverTests.cs

@@ -442,5 +442,28 @@ static void testSetHintAndSolverGetters()
 
         solver.SetHint(new Variable[] { x, y }, new double[] { 2.0, 3.0 });
     }
+
+    [Fact]
+    static void Given_a_LinearExpr_and_a_solution_When_SolutionValue_is_called_then_the_result_is_correct()
+    {
+        Console.WriteLine(nameof(Given_a_LinearExpr_and_a_solution_When_SolutionValue_is_called_then_the_result_is_correct));
+        Solver solver = Solver.CreateSolver("glop");
+        // x, y and z are fixed; we don't want to test the solver here.
+        Variable x = solver.MakeIntVar(3, 3, "x");
+        Variable y = solver.MakeIntVar(4, 4, "y");
+        Variable z = solver.MakeIntVar(5, 5, "z");
+
+        LinearExpr part1 = x * 2;         // 6
+        LinearExpr part2 = y * 3 + z + 4; // 21
+        LinearExpr objective = part1 + part2;   // 27
+        LinearExpr anew = new();
+        solver.Maximize(objective);
+        solver.Solve();
+        Assert.Equal(27, objective.SolutionValue(), precision: 9);
+        Assert.Equal(6, part1.SolutionValue(), precision: 9);
+        Assert.Equal(21, part2.SolutionValue(), precision: 9);
+        Assert.Equal(0, anew.SolutionValue(), precision: 9);
+        Assert.Equal(27, (objective + anew).SolutionValue(), precision: 9);
+    }
 }
 } // namespace Google.OrTools.Tests