Optimization is generating error plotting pareto front

The following code is generating the following error,

>> main
Optimization terminated: average change in the spread of Pareto 
solutions less than options.TolFun.
Undefined function or variable 'y'.

Error in main (line 9)
f1 = x.^4 + y.^4 - x.^2 * y.^2 + x * y - 10 * x.^2;

simpleMultiObjective.m

 function z = simpleMultiObjective(xy)
    x = xy(1); y = xy(2);
    z(1) = x.^4 + y.^4 - x.^2 * y.^2 + x * y - 10 * x.^2;    
    z(2) = x.^4 + y.^4 - x.^2 * y.^2 + x * y;
 end

main.m

fitness = @simpleMultiObjective;
nvar = 2;

[x, fval] = gamultiobj(fitness, nvar);

x0 = -5:0.5:5;

f1 = x.^4 + y.^4 - x.^2 * y.^2 + x * y - 10 * x.^2; 
f2 = x.^4 + y.^4 - x.^2 * y.^2 + x * y;

figure; hold on
plot(x0, f1);
plot(x0, f2);
grid;
xlabel('x');
ylabel('f');

plot(x, fval(:, 1), 'x');
plot(x, fval(:, 2), 'o');

figure;
plot(fval(:, 1), fval(:,2), 'o');
xlabel('f1');
ylabel('f2');
grid;

Answer 1

[Walter Roberson]

Change

[x, fval] = gamultiobj(fitness, nvar);

to

[xy, fval] = gamultiobj(fitness, nvar);
x = xy(1); y = xy(2);

[Ba Ba Black Sheep!]

How can I generate the table for data values for the Pareto front?

[Walter Roberson]

What table? The answer to what you calculated is a particular pair of values that is the pareto optimum. There is no "table" associated with a pair of values.