Module miplearn.problems.tests.test_stab

#  MIPLearn: Extensible Framework for Learning-Enhanced Mixed-Integer Optimization
#  Copyright (C) 2020, UChicago Argonne, LLC. All rights reserved.
#  Released under the modified BSD license. See COPYING.md for more details.

import networkx as nx
import numpy as np
from scipy.stats import uniform, randint

from miplearn.problems.stab import MaxWeightStableSetInstance
from miplearn.solvers.learning import LearningSolver


def test_stab():
    graph = nx.cycle_graph(5)
    weights = [1.0, 1.0, 1.0, 1.0, 1.0]
    instance = MaxWeightStableSetInstance(graph, weights)
    solver = LearningSolver()
    stats = solver.solve(instance)
    assert stats["Lower bound"] == 2.0


def test_stab_generator_fixed_graph():
    np.random.seed(42)
    from miplearn.problems.stab import MaxWeightStableSetGenerator

    gen = MaxWeightStableSetGenerator(
        w=uniform(loc=50.0, scale=10.0),
        n=randint(low=10, high=11),
        p=uniform(loc=0.05, scale=0.0),
        fix_graph=True,
    )
    instances = gen.generate(1_000)
    weights = np.array([instance.weights for instance in instances])
    weights_avg_actual = np.round(np.average(weights, axis=0))
    weights_avg_expected = [55.0] * 10
    assert list(weights_avg_actual) == weights_avg_expected


def test_stab_generator_random_graph():
    np.random.seed(42)
    from miplearn.problems.stab import MaxWeightStableSetGenerator

    gen = MaxWeightStableSetGenerator(
        w=uniform(loc=50.0, scale=10.0),
        n=randint(low=30, high=41),
        p=uniform(loc=0.5, scale=0.0),
        fix_graph=False,
    )
    instances = gen.generate(1_000)
    n_nodes = [instance.graph.number_of_nodes() for instance in instances]
    n_edges = [instance.graph.number_of_edges() for instance in instances]
    assert np.round(np.mean(n_nodes)) == 35.0
    assert np.round(np.mean(n_edges), -1) == 300.0