implement MPModelProtoExport::WriteModelAsMpsFormat

ortools/linear_solver/BUILD.bazel

@@ -376,6 +376,7 @@ cc_library(
     deps = [
         ":linear_solver_cc_proto",
         "//ortools/base",
+        "//ortools/base:file",
         "//ortools/base:hash",
         "//ortools/base:map_util",
         "//ortools/util:fp_utils",
@@ -395,6 +396,7 @@ cc_binary(
         ":linear_solver",
         ":linear_solver_cc_proto",
         "//ortools/base",
+        "//ortools/base:file",
         "//ortools/lp_data:lp_parser",
         "//ortools/lp_data:model_reader",
         "//ortools/lp_data:mps_reader",

ortools/linear_solver/model_exporter.cc

@@ -22,6 +22,7 @@
 #include <vector>
 
 #include "absl/container/flat_hash_set.h"
+#include "absl/flags/flag.h"
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
 #include "absl/strings/ascii.h"
@@ -29,11 +30,12 @@
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_format.h"
 #include "absl/strings/string_view.h"
-#include "ortools/base/commandlineflags.h"
+#include "ortools/base/file.h"
+#include "ortools/base/helpers.h"
 #include "ortools/base/logging.h"
-#include "ortools/base/map_util.h"
+#include "ortools/base/options.h"
+#include "ortools/base/status_macros.h"
 #include "ortools/linear_solver/linear_solver.pb.h"
-#include "ortools/util/fp_utils.h"
 
 ABSL_FLAG(bool, lp_log_invalid_name, false, "DEPRECATED.");
 
@@ -91,7 +93,8 @@ class MPModelProtoExporter {
   bool ExportModelAsLpFormat(const MPModelExportOptions& options,
                              std::string* output);
   bool ExportModelAsMpsFormat(const MPModelExportOptions& options,
-                              std::string* output);
+                              std::string* output, File* output_file);
+  void FlushAndResetString(std::string* output, File* file);
 
  private:
   // Computes the number of continuous, integer and binary variables.
@@ -241,12 +244,32 @@ absl::StatusOr<std::string> ExportModelAsMpsFormat(
   }
   MPModelProtoExporter exporter(model);
   std::string output;
-  if (!exporter.ExportModelAsMpsFormat(options, &output)) {
+  if (!exporter.ExportModelAsMpsFormat(options, &output, nullptr)) {
     return absl::InvalidArgumentError("Unable to export model.");
   }
   return output;
 }
 
+absl::Status WriteModelAsMpsFormat(absl::string_view filename,
+                                   const MPModelProto& model,
+                                   const MPModelExportOptions& options) {
+  if (model.general_constraint_size() > 0) {
+    return absl::InvalidArgumentError("General constraints are not supported.");
+  }
+  File* file;
+  RETURN_IF_ERROR(file::Open(filename, "w", &file, file::Defaults()));
+
+  absl::Status status = absl::OkStatus();
+  MPModelProtoExporter exporter(model);
+  std::string output;
+  if (!exporter.ExportModelAsMpsFormat(options, &output, file)) {
+    status.Update(file->Close(file::Defaults()));  // Even if Write() fails!
+    return absl::InvalidArgumentError("Unable to export model.");
+  }
+  status.Update(file->Close(file::Defaults()));
+  return status;
+}
+
 namespace {
 MPModelProtoExporter::MPModelProtoExporter(const MPModelProto& model)
     : proto_(model),
@@ -740,8 +763,17 @@ void MPModelProtoExporter::AppendMpsColumns(
   }
 }
 
+void MPModelProtoExporter::FlushAndResetString(std::string* output,
+                                               File* output_file) {
+  if (output_file == nullptr) return;
+  if (output->empty()) return;
+  CHECK_OK(file::WriteString(output_file, *output, file::Defaults()));
+  output->clear();
+}
+
 bool MPModelProtoExporter::ExportModelAsMpsFormat(
-    const MPModelExportOptions& options, std::string* output) {
+    const MPModelExportOptions& options, std::string* output,
+    File* output_file) {
   output->clear();
   Setup();
   ComputeMpsSmartColumnWidths(options.obfuscate);
@@ -787,6 +819,7 @@ bool MPModelProtoExporter::ExportModelAsMpsFormat(
   if (!rows_section.empty()) {
     absl::StrAppend(output, "ROWS\n", rows_section);
   }
+  FlushAndResetString(output, output_file);
 
   // As the information regarding a column needs to be contiguous, we create
   // a vector associating a variable index to a vector containing the indices
@@ -825,6 +858,7 @@ bool MPModelProtoExporter::ExportModelAsMpsFormat(
   if (!columns_section.empty()) {
     absl::StrAppend(output, "COLUMNS\n", columns_section);
   }
+  FlushAndResetString(output, output_file);
 
   // RHS (right-hand-side) section.
   current_mps_column_ = 0;
@@ -850,6 +884,7 @@ bool MPModelProtoExporter::ExportModelAsMpsFormat(
   if (!rhs_section.empty()) {
     absl::StrAppend(output, "RHS\n", rhs_section);
   }
+  FlushAndResetString(output, output_file);
 
   // RANGES section.
   current_mps_column_ = 0;
@@ -866,6 +901,7 @@ bool MPModelProtoExporter::ExportModelAsMpsFormat(
   if (!ranges_section.empty()) {
     absl::StrAppend(output, "RANGES\n", ranges_section);
   }
+  FlushAndResetString(output, output_file);
 
   // BOUNDS section.
   current_mps_column_ = 0;
@@ -926,8 +962,10 @@ bool MPModelProtoExporter::ExportModelAsMpsFormat(
   if (!bounds_section.empty()) {
     absl::StrAppend(output, "BOUNDS\n", bounds_section);
   }
+  FlushAndResetString(output, output_file);
 
   absl::StrAppend(output, "ENDATA\n");
+  FlushAndResetString(output, output_file);
   return true;
 }
 

ortools/linear_solver/model_exporter.h

@@ -16,7 +16,9 @@
 
 #include <string>
 
+#include "absl/status/status.h"
 #include "absl/status/statusor.h"
+#include "absl/strings/string_view.h"
 #include "ortools/linear_solver/linear_solver.pb.h"
 
 namespace operations_research {
@@ -95,6 +97,35 @@ absl::StatusOr<std::string> ExportModelAsMpsFormat(
     const MPModelProto& model,
     const MPModelExportOptions& options = MPModelExportOptions());
 
+/**
+ * Write the current model (variables, constraints, objective) to a file in MPS
+ * file format, using the "free" MPS format.
+ *
+ * Returns false if some error has occurred during execution. Models with
+ * maximization objectives trigger an error, because MPS can encode only
+ * minimization problems.
+ *
+ * The validity of names is automatically checked. If a variable name or a
+ * constraint name is invalid or non-existent, a new valid name is
+ * automatically generated.
+ *
+ * Name validity and obfuscation works exactly as in ExportModelAsLpFormat().
+ *
+ * For more information about the MPS format:
+ * http://en.wikipedia.org/wiki/MPS_(format)
+ * A close-to-original description coming from OSL:
+ * http://tinyurl.com/mps-format-by-osl
+ * A recent description from CPLEX:
+ * http://tinyurl.com/mps-format-by-cplex
+ * CPLEX extensions:
+ * http://tinyurl.com/mps-extensions-by-cplex
+ * Gurobi's description:
+ * http://www.gurobi.com/documentation/5.1/reference-manual/node869
+ */
+absl::Status WriteModelAsMpsFormat(
+    absl::string_view filename, const MPModelProto& model,
+    const MPModelExportOptions& options = MPModelExportOptions());
+
 }  // namespace operations_research
 
 #endif  // OR_TOOLS_LINEAR_SOLVER_MODEL_EXPORTER_H_

ortools/linear_solver/solve.cc

@@ -55,10 +55,12 @@
 #include <string>
 #include <utility>
 
+#include "absl/flags/declare.h"
 #include "absl/flags/flag.h"
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
 #include "absl/strings/match.h"
+#include "absl/strings/str_cat.h"
 #include "absl/strings/str_format.h"
 #include "absl/time/time.h"
 #include "ortools/base/file.h"
@@ -68,6 +70,7 @@
 #include "ortools/base/options.h"
 #include "ortools/linear_solver/linear_solver.h"
 #include "ortools/linear_solver/linear_solver.pb.h"
+#include "ortools/linear_solver/model_exporter.h"
 #include "ortools/lp_data/lp_parser.h"
 #include "ortools/lp_data/mps_reader.h"
 #include "ortools/lp_data/sol_reader.h"
@@ -114,6 +117,8 @@ ABSL_FLAG(std::string, dump_response, "",
           "If non-empty, dumps MPSolutionResponse there.");
 ABSL_FLAG(std::string, sol_file, "",
           "If non-empty, output the best solution in Miplib .sol format.");
+ABSL_FLAG(std::string, dump_mps, "",
+          "If non-empty, dumps the model in mps format there.");
 
 ABSL_DECLARE_FLAG(bool, verify_solution);  // Defined in ./linear_solver.cc
 ABSL_DECLARE_FLAG(bool,
@@ -310,6 +315,11 @@ void Run() {
                << absl::GetFlag(FLAGS_dump_format);
   }
 
+  if (!absl::GetFlag(FLAGS_dump_mps).empty()) {
+    CHECK_OK(WriteModelAsMpsFormat(absl::GetFlag(FLAGS_dump_mps),
+                                   request_proto.model()));
+  }
+
   // Set or override request proto options from the command line flags.
   if (type.has_value() || !request_proto.has_solver_type()) {
     request_proto.set_solver_type(static_cast<MPModelRequest::SolverType>(