gamultiobj output function error -- too many output arguments

I used 'gamultiobj' for a multi-objective task. I have two objectives and I would like to save the results of each iteration as the output. But Matlab gave me a warning says 'too many output arguments'

here is my code:

% Define the objective function for NSGA-II optimization
objectiveFunction = @(x) plateObjective(x);

% Define the number of design variables
numVariables = 3;

% Define lower and upper bounds for the design variables
lb = [20, 10, 2]; % Lower bounds for width, radius, and thickness
ub = [100, 50, 10]; % Upper bounds for width, radius, and thickness

% Define options for the NSGA-II algorithm
options = optimoptions('gamultiobj', ...
    'PopulationSize', 100, ...
    'MaxGenerations', 100, ...
    'FunctionTolerance', 1e-4, ...
    'PlotFcn', @gaplotpareto, ...
    'OutputFcns', @outputfunction);

% Run NSGA-II optimization
[xOptimal, fvalOptimal, exitflag, output, population, scores] = gamultiobj(objectiveFunction, numVariables, [], [], [], [], lb, ub, options);

options = optimoptions('ga','OutputFcn',{@myfun1,@myfun2});
    
function stop = outputfunction(options, state, flag)
    persistent history

    stop = false;

    switch flag
        case 'init'
            history = struct('generation', [], 'population', [], 'scores', []);
        case 'iter'
            % Append current generation, population, and scores to the history
            history.generation = [history.generation; state.Generation];
            history.population = [history.population; state.Population];
            history.scores = [history.scores; state.Score];
        case 'done'
            % Save the final generation, population, and scores
            history.generation = [history.generation; state.Generation];
            history.population = [history.population; state.Population];
            history.scores = [history.scores; state.Score];
            
            % Save the history structure to a file (you can customize the filename)
            save('optimization_history.mat', 'history');
    end
end

% Function to define the objective for NSGA-II
function f = plateObjective(x)

    % x(1): Width, x(2): Radius, x(3): Thickness
    % Set the dimensions
    MyWidth = x(1);
    MyRadius = x(2);
    MyThickness = x(3);
    
    % Check the constraint: MyWidth > MyRadius
    if MyWidth <= MyRadius
        % Penalize the objective for violating the constraint
        penalty = 1e6; % Set penalty value 
        f = [penalty, 0]; % Ask optimizer to avoid this solution
        return;
    end

    % Write dimensions to input.txt
    vals = [MyWidth, MyRadius, MyThickness];
    fileID = fopen('input.txt', 'w');
    fprintf(fileID, '%i\n %i\n %0.2f', vals);
    fclose(fileID);

    % Run Abaqus simulation
    system('abaqus cae nogui=abaqus_script_platehole.py -- PlateHole');

    % Read maximum von Mises stress from output.txt
    fileID = fopen('output.txt', 'r');
    S_vm_max = fscanf(fileID, '%f');
    fclose(fileID);

    % Calculate plate weight (you may need to customize this based on your specific problem)
    plateWeight = (MyWidth^2-pi*MyRadius^2)*MyThickness*2700;

    % Define the objective vector for NSGA-II
    f = [S_vm_max, plateWeight];
end

Answer 1

[Aditya]

Hi Zixuan,

It seems you're facing a problem with the ‘gamultiobj’ function, specifically encountering a 'too many output arguments' error.

This error typically occurs when the output function specified in the options for ‘gamultiobj’ does not match the expected signature.

The output function for ‘gamultiobj’ should return three output arguments: state, options, and stop. Here's the correct structure for the output function:

function [state, options, stop] = outputfunction(options, state, flag) 
end 

Hope this helps!