Add empty stubs for Highs support, #3116

ortools/linear_solver/linear_solver.h

@@ -199,10 +199,12 @@ class MPSolver {
     // gradient method. Sometimes faster than Glop for medium-size problems and
     // scales to much larger problems than Glop.
     PDLP_LINEAR_PROGRAMMING = 8,
+    HIGHS_LINEAR_PROGRAMMING = 15,
 
     // Integer programming problems.
     // -----------------------------
-    SCIP_MIXED_INTEGER_PROGRAMMING = 3,  // Recommended default value.
+    // Recommended default value for MIP problems.
+    SCIP_MIXED_INTEGER_PROGRAMMING = 3,
     GLPK_MIXED_INTEGER_PROGRAMMING = 4,
     CBC_MIXED_INTEGER_PROGRAMMING = 5,
 
@@ -214,13 +216,17 @@ class MPSolver {
     XPRESS_LINEAR_PROGRAMMING = 101,
     XPRESS_MIXED_INTEGER_PROGRAMMING = 102,
 
+    HIGHS_MIXED_INTEGER_PROGRAMMING = 16,
+
     // Boolean optimization problem (requires only integer variables and works
     // best with only Boolean variables).
     BOP_INTEGER_PROGRAMMING = 12,
 
     // SAT based solver (requires only integer and Boolean variables).
     // If you pass it mixed integer problems, it will scale coefficients to
     // integer values, and solver continuous variables as integral variables.
+    //
+    // Recommended default value for pure integral problems problems.
     SAT_INTEGER_PROGRAMMING = 14,
 
     // Dedicated knapsack solvers.

ortools/linear_solver/linear_solver.proto

@@ -425,6 +425,7 @@ message MPModelRequest {
     XPRESS_LINEAR_PROGRAMMING =
         101;                        // Commercial, needs a valid license. NOLINT
     CPLEX_LINEAR_PROGRAMMING = 10;  // Commercial, needs a valid license. NOLINT
+    HIGHS_LINEAR_PROGRAMMING = 15;
 
     SCIP_MIXED_INTEGER_PROGRAMMING = 3;  // Recommended default for MIP models.
     GLPK_MIXED_INTEGER_PROGRAMMING = 4;
@@ -434,13 +435,14 @@ message MPModelRequest {
         102;  // Commercial, needs a valid license. NOLINT
     CPLEX_MIXED_INTEGER_PROGRAMMING =
         11;  // Commercial, needs a valid license. NOLINT
+    HIGHS_MIXED_INTEGER_PROGRAMMING = 16;
     BOP_INTEGER_PROGRAMMING = 12;
 
     // WARNING: This solver will currently interpret all variables as integer,
     // so any solution you get will be valid, but the optimal might be far away
     // for the real one (when you authorise non-integer value for continuous
     // variables).
-    SAT_INTEGER_PROGRAMMING = 14;
+    SAT_INTEGER_PROGRAMMING = 14;  // Recommended for pure integer problems.
 
     // In-house linear programming solver based on the primal-dual hybrid
     // gradient method. Sometimes faster than Glop for medium-size problems and

ortools/linear_solver/proto_solver/BUILD.bazel

@@ -19,13 +19,15 @@ cc_library(
     name = "proto_solver",
     srcs = [
         "gurobi_proto_solver.cc",
+        "highs_proto_solver.cc",
         "pdlp_proto_solver.cc",
         "sat_proto_solver.cc",
         "sat_solver_utils.cc",
         "scip_proto_solver.cc",
     ],
     hdrs = [
         "gurobi_proto_solver.h",
+        "highs_proto_solver.h",
         "pdlp_proto_solver.h",
         "sat_proto_solver.h",
         "sat_solver_utils.h",
@@ -34,6 +36,7 @@ cc_library(
     copts = [
         "-DUSE_PDLP",
         "-DUSE_SCIP",
+        "-DUSE_HIGHS",
     ],
     deps = [
         "//ortools/base",

ortools/linear_solver/proto_solver/highs_proto_solver.cc

@@ -0,0 +1,37 @@
+// Copyright 2010-2022 Google LLC
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "ortools/linear_solver/proto_solver/highs_proto_solver.h"
+
+#include <cmath>
+#include <cstdint>
+#include <functional>
+#include <memory>
+#include <string>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include "absl/status/statusor.h"
+#include "ortools/linear_solver/linear_solver.pb.h"
+#include "ortools/linear_solver/model_validator.h"
+#include "ortools/port/proto_utils.h"
+
+namespace operations_research {
+
+absl::StatusOr<MPSolutionResponse> HighsSolveProto(MPModelRequest request,
+                                                   bool solve_as_a_mip) {
+  return absl::UnimplementedError("Highs support is not yet implemented");
+}
+
+}  // namespace operations_research

ortools/linear_solver/proto_solver/highs_proto_solver.h

@@ -0,0 +1,31 @@
+// Copyright 2010-2022 Google LLC
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#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 "absl/status/statusor.h"
+#include "ortools/linear_solver/linear_solver.pb.h"
+
+namespace operations_research {
+
+// Solve the input MIP model with the HIGHS solver.
+absl::StatusOr<MPSolutionResponse> HighsSolveProto(MPModelRequest request,
+                                                   bool solve_as_a_mip = true);
+
+}  // namespace operations_research
+
+#endif  // OR_TOOLS_LINEAR_SOLVER_PROTO_SOLVER_HIGHS_PROTO_SOLVER_H_

ortools/linear_solver/wrappers/BUILD.bazel

@@ -30,8 +30,9 @@ cc_library(
     srcs = ["model_builder_helper.cc"],
     hdrs = ["model_builder_helper.h"],
     copts = [
-        "-DUSE_SCIP",
-    ],
+        "-DUSE_HIGHS",
+        "-DUSE_PDLP",
+        "-DUSE_SCIP",    ],
     visibility = ["//visibility:public"],
     deps = [
         "//ortools/linear_solver",

ortools/linear_solver/wrappers/model_builder_helper.cc

@@ -21,6 +21,7 @@
 
 #include "ortools/linear_solver/linear_solver.h"
 #include "ortools/linear_solver/linear_solver.pb.h"
+#include "ortools/linear_solver/proto_solver/highs_proto_solver.h"
 #include "ortools/linear_solver/proto_solver/sat_proto_solver.h"
 #if defined(USE_SCIP)
 #include "ortools/linear_solver/proto_solver/scip_proto_solver.h"
@@ -324,6 +325,22 @@ void ModelSolverHelper::Solve(const ModelBuilderHelper& model) {
       break;
     }
 #endif  // defined(USE_SCIP)
+#if defined(USE_HIGHS)
+    case MPModelRequest::HIGHS_MIXED_INTEGER_PROGRAMMING: {
+      const auto temp = HighsSolveProto(request, true);
+      if (temp.ok()) {
+        response_ = std::move(temp.value());
+      }
+      break;
+    }
+    case MPModelRequest::HIGHS_LINEAR_PROGRAMMING: {
+      const auto temp = HighsSolveProto(request, false);
+      if (temp.ok()) {
+        response_ = std::move(temp.value());
+      }
+      break;
+    }
+#endif  // defined(USE_HIGHS)
     default: {
       response_->set_status(
           MPSolverResponseStatus::MPSOLVER_SOLVER_TYPE_UNAVAILABLE);

ortools/linear_solver/xpress_interface.cc

@@ -177,7 +177,7 @@ class XpressInterface : public MPSolverInterface {
       return 0.0;
     }
 
-    // TODO(user,user): Not yet working.
+    // TODO(user): Not yet working.
     LOG(DFATAL) << "ComputeExactConditionNumber not implemented for"
                 << " XPRESS_LINEAR_PROGRAMMING";
     return 0.0;