GA optimasation error during the running , the subcript indices must be integer positive or logical?

i define my fiteness function for the GA using 'assignin' expression

function [y]=myfiteness(x)

assignin('base','na',x(1));

assignin('base','nb',x(2));

[~,~,Y]=sim('mymodel',[0,1]);

y=y(end,2);

after using otimtool for GA for the function , the running stops and a message apear in the running section of the optimtool which show the following ''the subcript indices must be integer positive or logical''

so how to solve this problem????????

[Walter Roberson]

y=y(end,2);

You do not have variable y at that point, you have Y

What happens if Y is empty?

[khelifa siham]

thank you sir for your observation but in fact the variable is y, not Y as i wrote before, i made the mistake of writting while i was posting the question ,so there is variable to work with in the simulation.

[Walter Roberson]

What happens if sim() returns an empty variable at that point?