Source code for qrisp.qaoa.problems.maxClique

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"""Implements the QAOA cost function and problem setup for the maximum clique problem."""

import itertools

import networkx as nx

from qrisp.algorithms.qaoa.problems.maxIndepSet import (
    create_max_indep_set_cl_cost_function,
    create_max_indep_set_mixer,
    max_indep_set_init_function,
)



[docs]
def create_max_clique_cl_cost_function(G):
    """Creates the classical cost function for an instance of the maximum clique problem for a given graph ``G``.

    Parameters
    ----------
    G : nx.Graph
        The Graph for the problem instance.

    Returns
    -------
    cl_cost_function : function
        The classical cost function for the problem instance, which takes a dictionary of measurement results as input.

    """

    def cl_cost_function(res_dic):
        cost = 0
        for state, prob in res_dic.items():
            temp = True
            indices = [index for index, value in enumerate(state) if value == "1"]
            combinations = list(itertools.combinations(indices, 2))
            for combination in combinations:
                if combination not in G.edges():
                    temp = False
                    break
            if temp:
                cost += -len(indices) * prob

        return cost

    return cl_cost_function




[docs]
def max_clique_problem(G):
    """Creates a QAOA problem instance with appropriate phase separator, mixer, and
    classical cost function.

    Parameters
    ----------
    G : nx.Graph
        The graph for the problem instance.

    Returns
    -------
    :ref:`QAOAProblem`
        A QAOA problem instance for MaxClique for a given graph ``G``.

    """
    from qrisp.qaoa import QAOAProblem, RZ_mixer

    G_complement = nx.complement(G)

    return QAOAProblem(
        cost_operator=RZ_mixer,
        mixer=create_max_indep_set_mixer(G_complement),
        cl_cost_function=create_max_indep_set_cl_cost_function(G_complement),
        init_function=max_indep_set_init_function,
    )