# ___________________________________________________________________________
#
# Pyomo: Python Optimization Modeling Objects
# Copyright (c) 2008-2024
# 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.
# ___________________________________________________________________________
"""
This module contains functions for computing an irreducible infeasible set
for a Pyomo MILP or LP using a specified commercial solver, one of CPLEX,
Gurobi, or Xpress.
"""
import abc
import logging
from pyomo.environ import SolverFactory
logger = logging.getLogger("pyomo.contrib.iis")
logger.setLevel(logging.INFO)
[docs]def write_iis(pyomo_model, iis_file_name, solver=None, logger=logger):
"""
Write an irreducible infeasible set for a Pyomo MILP or LP
using the specified commercial solver.
Arguments
---------
pyomo_model:
A Pyomo Block or ConcreteModel
iis_file_name:str
A file name to write the IIS to, e.g., infeasible_model.ilp
solver:str
Specify the solver to use, one of "cplex", "gurobi", or "xpress".
If None, the tool will use the first solver available.
logger:logging.Logger
A logger for messages. Uses pyomo.contrib.iis logger by default.
Returns
-------
iis_file_name:str
The file containing the IIS.
"""
available_solvers = [
s
for s, sp in zip(_supported_solvers, _supported_solvers_persistent)
if SolverFactory(sp).available(exception_flag=False)
]
if solver is None:
if len(available_solvers) == 0:
raise RuntimeError(
f"Could not find a solver to use, supported solvers are {_supported_solvers}"
)
solver = available_solvers[0]
logger.info(f"Using solver {solver}")
else:
# validate
solver = solver.lower()
solver = _remove_suffix(solver, "_persistent")
if solver not in available_solvers:
raise RuntimeError(
f"The Pyomo persistent interface to {solver} could not be found."
)
solver_name = solver
solver = SolverFactory(solver + "_persistent")
solver.set_instance(pyomo_model, symbolic_solver_labels=True)
iis = IISFactory(solver)
iis.compute()
iis_file_name = iis.write(iis_file_name)
logger.info(f"IIS written to {iis_file_name}")
return iis_file_name
def _remove_suffix(string, suffix):
if string.endswith(suffix):
return string[: -len(suffix)]
else:
return string
class _IISBase(abc.ABC):
def __init__(self, solver):
self._solver = solver
@abc.abstractmethod
def compute(self):
"""computes the IIS/Conflict"""
pass
@abc.abstractmethod
def write(self, file_name):
"""writes the IIS in LP format
return the file name written
"""
pass
class CplexConflict(_IISBase):
def compute(self):
self._solver._solver_model.conflict.refine()
def write(self, file_name):
self._solver._solver_model.conflict.write(file_name)
return file_name
class GurobiIIS(_IISBase):
def compute(self):
self._solver._solver_model.computeIIS()
def write(self, file_name):
# gurobi relies on the suffix to
# determine the file type
file_name = _remove_suffix(file_name, ".ilp")
file_name += ".ilp"
self._solver._solver_model.write(file_name)
return file_name
class XpressIIS(_IISBase):
def compute(self):
self._solver._solver_model.iisfirst(1)
def write(self, file_name):
self._solver._solver_model.iiswrite(0, file_name, 0, "l")
if self._solver._version[0] < 38:
return file_name
else:
return _remove_suffix(file_name, ".lp") + ".lp"
_solver_map = {
"cplex_persistent": CplexConflict,
"gurobi_persistent": GurobiIIS,
"xpress_persistent": XpressIIS,
}
def IISFactory(solver):
if solver.name not in _solver_map:
raise RuntimeError(f"Unrecognized solver {solver.name}")
return _solver_map[solver.name](solver)
_supported_solvers_persistent = list(_solver_map.keys())
_supported_solvers = [_remove_suffix(s, "_persistent") for s in _solver_map]