Support for upcoming knitro python package

pyomo/solvers/plugins/solvers/KNITROAMPL.py

@@ -0,0 +1,87 @@
+#  ___________________________________________________________________________
+#
+#  Pyomo: Python Optimization Modeling Objects
+#  Copyright (c) 2008-2025
+#  National Technology and Engineering Solutions of Sandia, LLC
+#  Under the terms of Contract DE-NA0003525 with National Technology and
+#  Engineering Solutions of Sandia, LLC, the U.S. Government retains certain
+#  rights in this software.
+#  This software is distributed under the 3-clause BSD License.
+#  ___________________________________________________________________________
+import logging
+from pathlib import Path
+
+from pyomo.common import Executable
+from pyomo.common.collections import Bunch
+from pyomo.opt.base.formats import ProblemFormat, ResultsFormat
+from pyomo.opt.base.solvers import SolverFactory, OptSolver
+from pyomo.solvers.plugins.solvers.ASL import ASL
+
+logger = logging.getLogger('pyomo.solvers')
+
+
+@SolverFactory.register(
+    'knitroampl', doc='The Knitro solver for NLP/MINLP and their subclasses'
+)
+class KNITROAMPL(ASL):
+    """An interface to the Knitro optimizer that uses the AMPL Solver Library."""
+
+    def __init__(self, **kwds):
+        """Constructor"""
+        executable = kwds.pop('executable', None)
+        validate = kwds.pop('validate', True)
+        kwds["type"] = "knitroampl"
+        kwds["options"] = {'solver': "knitroampl"}
+        OptSolver.__init__(self, **kwds)
+        self._keepfiles = False
+        self._results_file = None
+        self._timer = ''
+        self._user_executable = None
+        # broadly useful for reporting, and in cases where
+        # a solver plugin may not report execution time.
+        self._last_solve_time = None
+        self._define_signal_handlers = None
+        self._version_timeout = 2
+
+        if executable == 'knitroampl':
+            self.set_executable(name=None, validate=validate)
+        elif executable is not None:
+            self.set_executable(name=executable, validate=validate)
+        #
+        # Setup valid problem formats, and valid results for each problem format.
+        # Also set the default problem and results formats.
+        #
+        self._valid_problem_formats = [ProblemFormat.nl]
+        self._valid_result_formats = {ProblemFormat.nl: [ResultsFormat.sol]}
+        self.set_problem_format(ProblemFormat.nl)
+        #
+        # Note: Undefined capabilities default to 'None'
+        #
+        self._capabilities = Bunch()
+        self._capabilities.linear = True
+        self._capabilities.integer = True
+        self._capabilities.quadratic_objective = True
+        self._capabilities.quadratic_constraint = True
+        self._capabilities.sos1 = False
+        self._capabilities.sos2 = False
+
+    def _default_executable(self):
+        try:
+            # If knitro Python package is available, use the executable it contains
+            import knitro
+
+            package_knitroampl_path = (
+                Path(knitro.__file__).resolve().parent / 'knitroampl' / 'knitroampl'
+            )
+            executable = Executable(str(package_knitroampl_path))
+        except ModuleNotFoundError:
+            # Otherwise, search usual path list
+            executable = Executable('knitroampl')
+        if not executable:
+            logger.warning(
+                "Could not locate the 'knitroampl' executable, "
+                "which is required for solver %s" % self.name
+            )
+            self.enable = False
+            return None
+        return executable.path()

pyomo/solvers/plugins/solvers/__init__.py

@@ -32,4 +32,5 @@
     xpress_direct,
     xpress_persistent,
     SAS,
+    KNITROAMPL,
 )

pyomo/solvers/tests/checks/test_KNITROAMPL.py

@@ -0,0 +1,140 @@
+#  ___________________________________________________________________________
+#
+#  Pyomo: Python Optimization Modeling Objects
+#  Copyright (c) 2008-2025
+#  National Technology and Engineering Solutions of Sandia, LLC
+#  Under the terms of Contract DE-NA0003525 with National Technology and
+#  Engineering Solutions of Sandia, LLC, the U.S. Government retains certain
+#  rights in this software.
+#  This software is distributed under the 3-clause BSD License.
+#  ___________________________________________________________________________
+
+from pyomo.common import unittest
+from pyomo.environ import (
+    ConcreteModel,
+    Var,
+    Objective,
+    Constraint,
+    Suffix,
+    NonNegativeIntegers,
+    NonNegativeReals,
+    value,
+)
+from pyomo.opt import SolverFactory, TerminationCondition
+
+knitroampl_available = SolverFactory('knitroampl').available(False)
+
+
+class TestKNITROAMPLInterface(unittest.TestCase):
+    @unittest.skipIf(
+        not knitroampl_available, "The 'knitroampl' command is not available"
+    )
+    def test_infeasible_lp(self):
+        with SolverFactory('knitroampl') as opt:
+            model = ConcreteModel()
+            model.X = Var(within=NonNegativeReals)
+            model.C1 = Constraint(expr=model.X == 1)
+            model.C2 = Constraint(expr=model.X == 2)
+            model.Obj = Objective(expr=model.X)
+
+            results = opt.solve(model)
+
+            self.assertEqual(
+                results.solver.termination_condition, TerminationCondition.infeasible
+            )
+
+    @unittest.skipIf(
+        not knitroampl_available, "The 'knitroampl' command is not available"
+    )
+    def test_unbounded_lp(self):
+        with SolverFactory('knitroampl') as opt:
+            model = ConcreteModel()
+            model.X = Var()
+            model.Obj = Objective(expr=model.X)
+
+            results = opt.solve(model)
+
+            self.assertIn(
+                results.solver.termination_condition,
+                (
+                    TerminationCondition.unbounded,
+                    TerminationCondition.infeasibleOrUnbounded,
+                ),
+            )
+
+    @unittest.skipIf(
+        not knitroampl_available, "The 'knitroampl' command is not available"
+    )
+    def test_optimal_lp(self):
+        with SolverFactory('knitroampl') as opt:
+            model = ConcreteModel()
+            model.X = Var(within=NonNegativeReals)
+            model.C1 = Constraint(expr=model.X >= 2.5)
+            model.Obj = Objective(expr=model.X)
+
+            results = opt.solve(model, load_solutions=True)
+
+            self.assertEqual(
+                results.solver.termination_condition, TerminationCondition.optimal
+            )
+            self.assertAlmostEqual(value(model.X), 2.5)
+
+    @unittest.skipIf(
+        not knitroampl_available, "The 'knitroampl' command is not available"
+    )
+    def test_get_duals_lp(self):
+        with SolverFactory('knitroampl') as opt:
+            model = ConcreteModel()
+            model.X = Var(within=NonNegativeReals)
+            model.Y = Var(within=NonNegativeReals)
+
+            model.C1 = Constraint(expr=2 * model.X + model.Y >= 8)
+            model.C2 = Constraint(expr=model.X + 3 * model.Y >= 6)
+
+            model.Obj = Objective(expr=model.X + model.Y)
+
+            results = opt.solve(model, suffixes=['dual'], load_solutions=False)
+
+            model.dual = Suffix(direction=Suffix.IMPORT)
+            model.solutions.load_from(results)
+
+            self.assertAlmostEqual(model.dual[model.C1], 0.4)
+            self.assertAlmostEqual(model.dual[model.C2], 0.2)
+
+    @unittest.skipIf(
+        not knitroampl_available, "The 'knitroampl' command is not available"
+    )
+    def test_infeasible_mip(self):
+        with SolverFactory('knitroampl') as opt:
+            model = ConcreteModel()
+            model.X = Var(within=NonNegativeIntegers)
+            model.C1 = Constraint(expr=model.X == 1)
+            model.C2 = Constraint(expr=model.X == 2)
+            model.Obj = Objective(expr=model.X)
+
+            results = opt.solve(model)
+
+            self.assertEqual(
+                results.solver.termination_condition, TerminationCondition.infeasible
+            )
+
+    @unittest.skipIf(
+        not knitroampl_available, "The 'knitroampl' command is not available"
+    )
+    def test_optimal_mip(self):
+        with SolverFactory('knitroampl') as opt:
+            model = ConcreteModel()
+            model.X = Var(within=NonNegativeIntegers)
+            model.C1 = Constraint(expr=model.X >= 2.5)
+            model.Obj = Objective(expr=model.X)
+
+            results = opt.solve(model, load_solutions=True)
+
+            self.assertEqual(
+                results.solver.termination_condition, TerminationCondition.optimal
+            )
+            self.assertAlmostEqual(value(model.X), 3)
+
+
+if __name__ == "__main__":
+    unittest.main()

pyomo/solvers/tests/mip/test4.soln

@@ -0,0 +1,3 @@
+MILP solution:
+Objective value = 2
+x2 = 1

pyomo/solvers/tests/testcases.py

@@ -285,8 +285,17 @@
 #
 # KNITROAMPL
 #
-# NO EXPECTED FAILURES
-#
+for prob in ('LP_trivial_constraints', 'LP_trivial_constraints_kernel'):
+    ExpectedFailures['knitroampl', 'nl', prob] = (
+        lambda v: True,
+        'Knitro does not consider tight trivial constraints to have zero dual value',
+    )
+
+for prob in ('MILP_unbounded', 'MILP_unbounded_kernel'):
+    ExpectedFailures['knitroampl', 'nl', prob] = (
+        lambda v: v[:2] <= (14, 2),
+        'Unbounded MILP detection not operational in Knitro, fixed in 15.0',
+    )
 
 
 def generate_scenarios(arg=None):