Fix //examples/cpp:integer_programming_test by implementing linear_solver::nodes() for HiGHS.

Author: gchatelet

ortools/linear_solver/highs_interface.cc

@@ -15,6 +15,7 @@
 
 #include <atomic>
 #include <cstdint>
+#include <optional>
 #include <string>
 #include <utility>
 #include <vector>
@@ -102,6 +103,7 @@ class HighsInterface : public MPSolverInterface {
   void NonIncrementalChange();
 
   const bool solve_as_a_mip_;
+  std::optional<HighsSolveInfo> solve_info_;
 };
 
 HighsInterface::HighsInterface(MPSolver* const solver, bool solve_as_a_mip)
@@ -140,8 +142,9 @@ MPSolver::ResultStatus HighsInterface::Solve(const MPSolverParameters& param) {
   }
 
   // Set parameters.
+  solve_info_ = HighsSolveInfo();
   absl::StatusOr<MPSolutionResponse> response =
-      HighsSolveProto(std::move(request));
+      HighsSolveProto(std::move(request), &*solve_info_);
 
   if (!response.ok()) {
     LOG(ERROR) << "Unexpected error solving with Highs: " << response.status();
@@ -163,7 +166,10 @@ MPSolver::ResultStatus HighsInterface::Solve(const MPSolverParameters& param) {
   return result_status_;
 }
 
-void HighsInterface::Reset() { ResetExtractionInformation(); }
+void HighsInterface::Reset() {
+  ResetExtractionInformation();
+  solve_info_.reset();
+}
 
 void HighsInterface::SetOptimizationDirection(bool maximize) {
   NonIncrementalChange();
@@ -215,8 +221,9 @@ int64_t HighsInterface::iterations() const {
 }
 
 int64_t HighsInterface::nodes() const {
-  LOG(DFATAL) << "Number of nodes only available for discrete problems";
-  return MPSolverInterface::kUnknownNumberOfNodes;
+  QCHECK(solve_info_.has_value())
+      << "Number of nodes only available after solve";
+  return solve_info_->mip_node_count;
 }
 
 MPSolver::BasisStatus HighsInterface::row_status(int constraint_index) const {

ortools/linear_solver/proto_solver/highs_proto_solver.cc

@@ -46,7 +46,7 @@ absl::Status SetSolverSpecificParameters(const std::string& parameters,
                                          Highs& highs);
 
 absl::StatusOr<MPSolutionResponse> HighsSolveProto(
-    LazyMutableCopy<MPModelRequest> request) {
+    LazyMutableCopy<MPModelRequest> request, HighsSolveInfo* solve_info) {
   MPSolutionResponse response;
   const std::optional<LazyMutableCopy<MPModelProto>> optional_model =
       GetMPModelOrPopulateResponse(request, &response);
@@ -262,6 +262,10 @@ absl::StatusOr<MPSolutionResponse> HighsSolveProto(
     }
   }
 
+  if (solve_info != nullptr) {
+    solve_info->mip_node_count = highs.getInfo().mip_node_count;
+  }
+
   const absl::Duration solving_duration = absl::Now() - time_before;
   user_timer.Stop();
   response.mutable_solve_info()->set_solve_wall_time_seconds(

ortools/linear_solver/proto_solver/highs_proto_solver.h

@@ -14,18 +14,24 @@
 #ifndef OR_TOOLS_LINEAR_SOLVER_PROTO_SOLVER_HIGHS_PROTO_SOLVER_H_
 #define OR_TOOLS_LINEAR_SOLVER_PROTO_SOLVER_HIGHS_PROTO_SOLVER_H_
 
-#include <functional>
-#include <string>
+#include <cstdint>
 
 #include "absl/status/statusor.h"
 #include "ortools/linear_solver/linear_solver.pb.h"
 #include "ortools/util/lazy_mutable_copy.h"
 
 namespace operations_research {
 
-// Solve the input MIP model with the HIGHS solver.
+// Information about the Highs solve.
+struct HighsSolveInfo {
+  int64_t mip_node_count;  // The number of nodes generated by the MIP solver.
+};
+
+// Solve the input MIP model with the HIGHS solver and fills `solve_info` is
+// provided.
 absl::StatusOr<MPSolutionResponse> HighsSolveProto(
-    LazyMutableCopy<MPModelRequest> request);
+    LazyMutableCopy<MPModelRequest> request,
+    HighsSolveInfo* solve_info = nullptr);
 
 }  // namespace operations_research