WHY SOMETIME THE PARETO SPREAD IS NAN VALUE. CAN YOU FIX THIS?
% Main script to run MOEMA optimization
clc; 
clear; 
close all;
% Set problem parameters
NPop = 50;  % Population size
T = 50;     % Number of iterations
dim = 30;    % Number of decision variables
lb = zeros(1, dim);  % Lower bound
ub = ones(1, dim);   % Upper bound

% Run MOEMA
[paretoFront, paretoSet, Trajectories, fitness_history, position_history] = MOEMA(NPop, T, lb, ub, dim, @zdt2);

% Plot the Pareto front
figure;
plot(paretoFront(:,1), paretoFront(:,2), 'ro');
xlabel('f1');
ylabel('f2');
title('Pareto Front for ZDT2 using MOEMA');

% Calculate and display metrics
disp(['Number of solutions in Pareto Front: ', num2str(size(paretoFront, 1))]);
disp(['Minimum f1: ', num2str(min(paretoFront(:,1)))]);
disp(['Minimum f2: ', num2str(min(paretoFront(:,2)))]);


function [paretoFront, paretoSet, Trajectories, fitness_history, position_history] = MOEMA(NPop, T, lb, ub, dim, FITNESSFCN)
% Multi-Objective Evolutionary Mating Algorithm (MOEMA)
% MOEMA attempts to solve multi-objective problems of the following form:
%  min F(X) = [f1(X), f2(X), ..., fm(X)]  subject to: lb <= X <= ub
%                  
%  FITNESSFCN   - function handle of the multi-objective fitness function
%  lb           - lower bounds on X
%  ub           - upper bounds on X
%  T            - number of iterations
%  NPop         - size of the population (class size)  
%  paretoFront  - set of non-dominated solutions in objective space
%  paretoSet    - set of non-dominated solutions in decision space
%  Trajectories - best solution trajectory over iterations
%  fitness_history - history of fitness values
%  position_history - history of population positions

% Preallocation
fitness_history = zeros(NPop, T, 2);  % Assuming 2 objectives
position_history = zeros(NPop, T, dim);
Trajectories = zeros(dim, T);

% Generation of initial population
pop = initialization(NPop, dim, ub, lb);
pop_dad = pop(1:NPop/2, :);  % Eqn (1) in the paper
pop_mum = pop(NPop/2+1:end, :); % Eqn (2) in the paper

% Evaluation of objective function for initialization
obj_dad = evaluate_population(pop_dad, FITNESSFCN);
obj_mum = evaluate_population(pop_mum, FITNESSFCN);
obj = [obj_dad; obj_mum];

% Initialize archive with non-dominated solutions
archive = update_archive([], [], pop, obj);

for gen = 1:T  % Start iteration
    k1 = randperm(NPop/2);
    k2 = randperm(NPop/2);
    k1x = pop_dad(k1, :);
    k2x = pop_mum(k2, :);
    
    for k = 1:NPop/2
        % Mating process
        Imates = 1 + (var(k1x(k, :)) - var(k2x(k, :))); % Eqn (4) in the paper
        p = randn(1, dim);  % Eqn (6) in the paper
        r = rand();
        
        if Imates >= 0  % Upper part of Eqn (5) in the paper
            temp1 = p .* k1x(k, :);
            temp2 = (1-p) .* k2x(k, :);
            pop_child = temp1 + temp2;
        else  % Lower part of Eqn (5) in the paper
            temp1 = p .* k2x(k, :);
            temp2 = (1-p) .* k1x(k, :);
            pop_child = temp1 + temp2;
        end
        
        % Impact of best environment (using random non-dominated solution)
        if ~isempty(archive.pop)
            best_pop = archive.pop(randi(size(archive.pop, 1)), :);
            K = rand(1, dim) < 0.8;  % Eqn (8) in the paper
            pop_child = best_pop .* (1-K) + pop_child .* K;  % Eqn (7) in the paper
        end
        
        % Bounding of the solution
        pop_child = max(min(ub, pop_child), lb);
        
        % Evaluate child
        obj_child = FITNESSFCN(pop_child);
        
        % Update population using non-dominated sorting
        [pop_dad, obj_dad] = update_population(pop_dad, obj_dad, pop_child, obj_child, k1(k));
        [pop_mum, obj_mum] = update_population(pop_mum, obj_mum, pop_child, obj_child, k2(k));
        
        % Exploration process
        if r < 0.2
            if ~isempty(archive.pop)
                temp1 = archive.pop(randi(size(archive.pop, 1)), :);
                pop_child = rand(1, dim) .* temp1;  % Eqn (9) in the paper
                pop_child = max(min(ub, pop_child), lb);
                obj_child = FITNESSFCN(pop_child);
                
                % Update population using non-dominated sorting
                [pop_dad, obj_dad] = update_population(pop_dad, obj_dad, pop_child, obj_child, randi(NPop/2));
                [pop_mum, obj_mum] = update_population(pop_mum, obj_mum, pop_child, obj_child, randi(NPop/2));
            end
        end
    end
    
    % Combine updated pool dad and mum
    pop = [pop_dad; pop_mum];
    obj = [obj_dad; obj_mum];
    
    % Update archive
    archive = update_archive(archive.pop, archive.obj, pop, obj);
    
    % Record the history at each iteration
    fitness_history(:, gen, :) = obj;
    position_history(:, gen, :) = pop;
    
    % Update Trajectories (using a random non-dominated solution)
    if ~isempty(archive.pop)
        Trajectories(:, gen) = archive.pop(randi(size(archive.pop, 1)), :)';
    end
    
    disp(['Iteration #', num2str(gen), ' completed. Archive size: ', num2str(size(archive.pop, 1))]);
end

% Return Pareto front and Pareto set
paretoFront = archive.obj;
paretoSet = archive.pop;

end

% Helper Functions

function pop = initialization(NPop, dim, ub, lb)
    pop = rand(NPop, dim) .* (ub - lb) + lb;
end

function obj = evaluate_population(pop, FITNESSFCN)
    obj = zeros(size(pop, 1), 2);  % Assuming 2 objectives
    for i = 1:size(pop, 1)
        obj(i, :) = FITNESSFCN(pop(i, :));
    end
end

function [pop, obj] = update_population(pop, obj, child, child_obj, index)
    if dominates(child_obj, obj(index, :))
        pop(index, :) = child;
        obj(index, :) = child_obj;
    elseif ~dominates(obj(index, :), child_obj)
        if rand() < 0.5
            pop(index, :) = child;
            obj(index, :) = child_obj;
        end
    end
end

function archive = update_archive(archive_pop, archive_obj, pop, obj)
    combined_pop = [archive_pop; pop];
    combined_obj = [archive_obj; obj];
    
    [is_dominated, ~] = pareto_dominance(combined_obj);
    non_dominated = ~is_dominated;
    
    archive.pop = combined_pop(non_dominated, :);
    archive.obj = combined_obj(non_dominated, :);
end

function [is_dominated, domination_count] = pareto_dominance(objectives)
    [n_solutions, n_objectives] = size(objectives);
    is_dominated = false(n_solutions, 1);
    domination_count = zeros(n_solutions, 1);

    for i = 1:n_solutions
        for j = i+1:n_solutions
            if dominates(objectives(i, :), objectives(j, :))
                is_dominated(j) = true;
                domination_count(i) = domination_count(i) + 1;
            elseif dominates(objectives(j, :), objectives(i, :))
                is_dominated(i) = true;
                domination_count(j) = domination_count(j) + 1;
            end
        end
    end
end

function result = dominates(obj1, obj2)
    result = all(obj1 <= obj2) && any(obj1 < obj2);
end

function f = zdt2(x)
    f1 = x(1);
    g = 1 + 9*sum(x(2:end))/(length(x)-1);
    f2 = g * (1 - (f1/g)^2);
    f = [f1, f2];
end