fix xpress

Author: Robbie Muir

doc/release_notes.rst

@@ -2,7 +2,7 @@ Release Notes
 =============
 
 .. Upcoming Version
-
+* xpress: Fixed for xpress v9.5 (broken since linopy v0.5.8), upgraded deprecated xpress methods
 * Add support for SOS1 and SOS2 (Special Ordered Sets) constraints via ``Model.add_sos_constraints()`` and ``Model.remove_sos_constraints()``
 * Add simplify method to LinearExpression to combine duplicate terms
 * Add convenience function to create LinearExpression from constant

linopy/solvers.py

@@ -1600,21 +1600,22 @@ def solve_problem_from_file(
             except Exception as err:
                 logger.info("Unable to save solution file. Raised error: %s", err)
 
-        condition = m.getProbStatusString()
+        condition: str = m.getAttrib("solstatus").name.lower()
         termination_condition = CONDITION_MAP.get(condition, condition)
         status = Status.from_termination_condition(termination_condition)
         status.legacy_status = condition
 
-        def get_solver_solution() -> Solution:
-            objective = m.getObjVal()
+        def get_solver_solution_new() -> Solution:
+            # For xpress >= 9.6
+            objective: float = m.getAttrib("objval")
 
-            var = m.getnamelist(xpress_Namespaces.COLUMN, 0, m.attributes.cols - 1)
+            var = m.getnamelist(xpress.Namespaces.COLUMN, 0, m.attributes.cols - 1)
             sol = pd.Series(m.getSolution(), index=var, dtype=float)
 
             try:
-                _dual = m.getDual()
+                _dual = m.getDuals()
                 constraints = m.getnamelist(
-                    xpress_Namespaces.ROW, 0, m.attributes.rows - 1
+                    xpress.Namespaces.ROW, 0, m.attributes.rows - 1
                 )
                 dual = pd.Series(_dual, index=constraints, dtype=float)
             except (xpress.SolverError, xpress.ModelError, SystemError):
@@ -1623,6 +1624,29 @@ def get_solver_solution() -> Solution:
 
             return Solution(sol, dual, objective)
 
+        def get_solver_solution_legacy() -> Solution:
+            # For xpress < 9.6
+            objective: float = m.getAttrib("objval")
+
+            var = [str(v) for v in m.getVariable()]
+
+            sol = pd.Series(m.getSolution(var), index=var, dtype=float)
+
+            try:
+                dual_ = [str(d) for d in m.getConstraint()]
+                dual = pd.Series(m.getDuals(dual_), index=dual_, dtype=float)
+            except (xpress.SolverError, xpress.ModelError, SystemError):
+                logger.warning("Dual values of MILP couldn't be parsed")
+                dual = pd.Series(dtype=float)
+
+            return Solution(sol, dual, objective)
+
+        def get_solver_solution() -> Solution:
+            if parse_version(xpress.__version__) >= parse_version("9.6"):
+                return get_solver_solution_new()
+            else:
+                return get_solver_solution_legacy()
+
         solution = self.safe_get_solution(status=status, func=get_solver_solution)
         solution = maybe_adjust_objective_sign(solution, io_api, sense)
 

test/test_optimization.py

@@ -10,6 +10,7 @@
 import itertools
 import logging
 from typing import Any
+from unittest.mock import patch
 
 import numpy as np
 import pandas as pd
@@ -641,6 +642,32 @@ def test_model_with_inf(
     assert (model_with_inf.solution.y == 10).all()
 
 
+@pytest.mark.skipif(
+    "xpress" not in available_solvers, reason="Xpress solver not available"
+)
+def test_old_xpress_version_no_dual(model_with_inf: Model) -> None:
+    # Confirm that the old code path for xpress 9.5.x still works (when duals are not available)
+    with patch("xpress.__version__", "9.5.0"):
+        _, condition = model_with_inf.solve("xpress")
+    assert condition == "optimal"
+    assert (model_with_inf.solution.x == 0).all()
+    assert (model_with_inf.solution.y == 10).all()
+    assert len(model_with_inf.dual.keys()) == 0
+
+
+@pytest.mark.skipif(
+    "xpress" not in available_solvers, reason="Xpress solver not available"
+)
+def test_old_xpress_version_with_dual(model: Model) -> None:
+    # Confirm that the old code path for xpress 9.5.x still works (when duals are available)
+    with patch("xpress.__version__", "9.5.0"):
+        status, condition = model.solve("xpress")
+    assert status == "ok"
+    assert condition == "optimal"
+    assert np.isclose(model.objective.value or 0, 3.3)
+    assert np.isclose(model.dual["con0"].values, 0.3)
+
+
 @pytest.mark.parametrize(
     "solver,io_api,explicit_coordinate_names",
     [p for p in params if p[0] not in ["mindopt"]],