From ebdbfc0166beff87f8676aec0843d3872da3c7a7 Mon Sep 17 00:00:00 2001
From: Peter Mitri <peter.mitri@rte-france.com>
Date: Thu, 23 Jan 2025 10:41:34 +0100
Subject: [PATCH] update dual status for specific case

---
 ortools/math_opt/solvers/xpress_solver.cc | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/ortools/math_opt/solvers/xpress_solver.cc b/ortools/math_opt/solvers/xpress_solver.cc
index 6a3988da86..c2e18ceee7 100644
--- a/ortools/math_opt/solvers/xpress_solver.cc
+++ b/ortools/math_opt/solvers/xpress_solver.cc
@@ -495,9 +495,13 @@ SolutionStatusProto XpressSolver::getDualSolutionStatus() const {
     case XPRS_SOLSTATUS_FEASIBLE:
       return SOLUTION_STATUS_FEASIBLE;
     case XPRS_SOLSTATUS_INFEASIBLE:
-      // when primal is unbounded, XPRESS returns unbounded for dual also
-    case XPRS_SOLSTATUS_UNBOUNDED:
       return SOLUTION_STATUS_INFEASIBLE;
+    case XPRS_SOLSTATUS_UNBOUNDED:
+      // when primal is unbounded, XPRESS returns unbounded for dual also (known
+      // issue). this is a temporary workaround
+      return (xpress_lp_status_.primal_status == XPRS_LP_UNBOUNDED)
+                 ? SOLUTION_STATUS_INFEASIBLE
+                 : SOLUTION_STATUS_UNDETERMINED;
     case XPRS_SOLSTATUS_NOTFOUND:
       return SOLUTION_STATUS_UNDETERMINED;
     default: