From 46ffc703e217c63c3ac4d229d020a74aa3408bf7 Mon Sep 17 00:00:00 2001
From: Andrea Sgattoni <andrea.sgattoni@rte-france.com>
Date: Fri, 22 Dec 2023 16:24:17 +0100
Subject: [PATCH] improve perf and fix error

---
 ortools/linear_solver/xpress_interface.cc     |  5 ++--
 .../linear_solver/xpress_interface_test.cc    | 25 +++++++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/ortools/linear_solver/xpress_interface.cc b/ortools/linear_solver/xpress_interface.cc
index d8877aff31..0fa937c2a6 100644
--- a/ortools/linear_solver/xpress_interface.cc
+++ b/ortools/linear_solver/xpress_interface.cc
@@ -840,8 +840,7 @@ XpressInterface::XpressInterface(MPSolver* const solver, bool mip)
       mLp(nullptr),
       mMip(mip),
       supportIncrementalExtraction(false),
-      slowUpdates(static_cast<SlowUpdates>(SlowSetObjectiveCoefficient |
-                                           SlowClearObjective)),
+      slowUpdates(SlowClearObjective),
       mapStringControls_(getMapStringControls()),
       mapDoubleControls_(getMapDoubleControls()),
       mapIntegerControls_(getMapIntControls()),
@@ -1728,7 +1727,7 @@ void XpressInterface::SetLpAlgorithm(int value) {
 std::vector<int> XpressBasisStatusesFrom(
     const std::vector<MPSolver::BasisStatus>& statuses) {
   std::vector<int> result;
-  result.reserve(statuses.size());
+  result.resize(statuses.size());
   std::transform(statuses.cbegin(), statuses.cend(), result.begin(),
                  MPSolverToXpressBasisStatus);
   return result;
diff --git a/ortools/linear_solver/xpress_interface_test.cc b/ortools/linear_solver/xpress_interface_test.cc
index 2c251824f6..e5c31d74ba 100644
--- a/ortools/linear_solver/xpress_interface_test.cc
+++ b/ortools/linear_solver/xpress_interface_test.cc
@@ -329,6 +329,31 @@ TEST(XpressInterface, LpStartingBasis) {
   EXPECT_LT(iterWithBasis, 10);
 }
 
+TEST(XpressInterface, LpStartingBasisNoIterationsIfBasisIsProvided) {
+  UNITTEST_INIT_LP();
+  buildLargeLp(solver, 1000);
+  // First, we record the number of iterations without an initial basis
+  solver.Solve();
+
+  // Then, we retrieve the final basis
+  std::vector<MPSolver::BasisStatus> varStatus, constrStatus;
+  for (auto* var : solver.variables()) {
+    varStatus.push_back(var->basis_status());
+  }
+  for (auto* constr : solver.constraints()) {
+    constrStatus.push_back(constr->basis_status());
+  }
+
+  MPSolver solver_BasisProvided("XPRESS_LP", MPSolver::XPRESS_LINEAR_PROGRAMMING);
+  buildLargeLp(solver_BasisProvided, 1000);
+  solver_BasisProvided.SetStartingLpBasis(varStatus, constrStatus);
+  solver_BasisProvided.Solve();
+  const auto iterWithBasis = solver_BasisProvided.iterations();
+  // ...and finally check that no iteration has been performed
+  EXPECT_EQ(iterWithBasis, 0);
+}
+
+
 TEST(XpressInterface, NumVariables) {
   UNITTEST_INIT_MIP();
   MPVariable* x1 = solver.MakeNumVar(-1., 5.1, "x1");