Add region tag to linear solver samples

ortools/linear_solver/samples/simple_lp_program.cc

@@ -13,34 +13,52 @@
 
 // Minimal example to call the GLOP solver.
 // [START program]
-#include <iostream>
+// [START import]
 #include "ortools/linear_solver/linear_solver.h"
+// [END import]
 
 namespace operations_research {
 void run() {
+  // [START solver]
   // Create the linear solver with the GLOP backend.
   MPSolver solver("simple_lp_program", MPSolver::GLOP_LINEAR_PROGRAMMING);
+  // [END solver]
 
+  // [START variables]
   // Create the variables x and y.
   MPVariable* const x = solver.MakeNumVar(0.0, 1, "x");
   MPVariable* const y = solver.MakeNumVar(0.0, 2, "y");
 
+  LOG(INFO) << "Number of variables = " << solver.NumVariables();
+  // [END variables]
+
+  // [START constraints]
   // Create a linear constraint, 0 <= x + y <= 2.
   MPConstraint* const ct = solver.MakeRowConstraint(0.0, 2.0, "ct");
   ct->SetCoefficient(x, 1);
   ct->SetCoefficient(y, 1);
 
+  LOG(INFO) << "Number of constraints = " << solver.NumConstraints();
+  // [END constraints]
+
+  // [START objective]
   // Create the objective function, 3 * x + y.
   MPObjective* const objective = solver.MutableObjective();
   objective->SetCoefficient(x, 3);
   objective->SetCoefficient(y, 1);
   objective->SetMaximization();
+  // [END objective]
 
-  // Call the solver and display the results.
+  // [START solve]
   solver.Solve();
+  // [END solve]
+
+  // [START print_solution]
   std::cout << "Solution:" << std::endl;
-  std::cout << "x = " << x->solution_value() << std::endl;
-  std::cout << "y = " << y->solution_value() << std::endl;
+  LOG(INFO) << "Objective value = " << objective->Value();
+  LOG(INFO) << "x = " << x->solution_value();
+  LOG(INFO) << "y = " << y->solution_value();
+  // [END print_solution]
 }
 }  // namespace operations_research