Pyomo hangs when running MAiNGO solver

[SolverMax]

Summary

Pyomo 6.7.2 added support for the MAiNGO solver. When running a simple model, Pyomo hangs, with no output or result.

Steps to reproduce the issue

I'm running the following model. If the solver is set to 'bonmin', then Pyomo returns the correct optimal solution of x = 2, z = -1. When the solver if set to 'maingo', Pyomo produces no output. In Task Manager, I can see that the MAiNGO.exe process is running and using the CPU, but it does not end.

import pyomo.environ as pyo
Model = pyo.ConcreteModel()
Model.x = pyo.Var(domain = pyo.Reals, bounds = (0, 8), initialize = 1)
z = -1 * pyo.exp(-((Model.x - 2)**2))
Model.Obj = pyo.Objective(expr = z, sense = pyo.minimize)
Solver = pyo.SolverFactory('maingo')
Results = Solver.solve(Model, load_solutions = True, tee = True)
print(f'\nx = {Model.x():7.4f}  z = {Model.Obj():7.4f}  {Results.solver.termination_condition}\n')

MAiNGO correctly solves the same model when written using its interface, as follows:

from maingopy import *
from math import pi

class Model(MAiNGOmodel):
    def __init__(self):
        MAiNGOmodel.__init__(self) # Should be there for technical reasons
    
    def get_variables(self):
        variables = [OptimizationVariable(Bounds(0,8), VT_CONTINUOUS, "x")  ]
        return variables

    def get_initial_point(self):
        initialPoint = [1]
        return initialPoint

    def evaluate(self, vars):
        x = vars[0]
        result = EvaluationContainer()
        result.objective = -1 * exp(-((x - 2)**2))
        result.ineq = [x - 8]   # x <= 8
        result.ineq = [-x]   # x >= 0
        result.output = [OutputVariable("Result of x: ", x)]
        return result

myModel = Model()
myMAiNGO = MAiNGO(myModel)
fileName = ""
myMAiNGO.read_settings(fileName) # If fileName is empty, MAiNGO will attempt to open MAiNGOSettings.txt
maingoStatus = myMAiNGO.solve()

Information on your system

Pyomo version: 6.7.2
Python version: 3.11.8
Operating system: Windows 11
How Pyomo was installed (PyPI, conda, source): PyPl
Solver (if applicable): MAiNGO

[mrmundt]

@SolverMax - Question: does the same thing happen if you do not have tee = True?

[SolverMax]

Yes. tee = True or False makes no difference.

[mrmundt]

@MAiNGO-github - FYI - issue regarding MAiNGO interface!

[MAiNGO-github]

@mrmundt We had a look at the issue.
To us it seems that the SolverFactory is not working properly.

@SolverMax Could you please try the following code and see if it still hangs without output?

import pyomo.environ as pyo
from pyomo.contrib.appsi.solvers import MAiNGO
 
Model = pyo.ConcreteModel()
Model.x = pyo.Var(domain=pyo.Reals, bounds=(0, 8), initialize=1)
z = -1 * pyo.exp(-((Model.x - 2) ** 2))
Model.Obj = pyo.Objective(expr=z, sense=pyo.minimize)
Solver = MAiNGO()
Solver.maingo_options["loggingDestination"] = 3
Results = Solver.solve(Model)
print(
    f"\nx = {Model.x():7.4f}  z = {Model.Obj():7.4f}  {Results.termination_condition}\n"
)

[SolverMax]

The revised model runs and produces the expected output:
x = 2.0000 z = -1.0000 TerminationCondition.optimal

[MAiNGO-github]

@mrmundt It seems to us, that MAiNGO is not registered to the default SolverFactory, but only to the appsi SolverFactory.
So this code using the appsi SolverFactory should work just fine.

import pyomo.environ as pyo
from pyomo.contrib.appsi.base import SolverFactory

Model = pyo.ConcreteModel()
Model.x = pyo.Var(domain=pyo.Reals, bounds=(0, 8), initialize=1)
z = -1 * pyo.exp(-((Model.x - 2) ** 2))
Model.Obj = pyo.Objective(expr=z, sense=pyo.minimize)
Solver = SolverFactory("maingo")
Solver.maingo_options["loggingDestination"] = 3
Results = Solver.solve(Model)
print(
    f"\nx = {Model.x():7.4f}  z = {Model.Obj():7.4f}  {Results.termination_condition}\n"
)

@mrmundt Is this intended behavior, or should MAiNGO also be registered to the default SolverFactory?