Index exceeds array dimensions. Index value 7 exceeds valid range [1-6] for array 'u'. Error in 'control/MATLAB Function' (line 8) y=u(row,:);

i would out of function is 0 in 6 out all time when theta_array is empty or first colloum is [0,0,0,0,0,0]

function y = fcn(u)

persistent row
if isempty(row)
    row=0;
end
row=row+1;
y=u(row,:);
end