hi every one I found the answer and I write that here maybe it be useful for others
clear,clc
a = 5;
b = ones(2);
x = zeros(2);
t3 = zeros(1,5);
for i = 1:5
tic
c = a*b;
k = x-2*c;
x = k;
s = 0.5-toc;
if sign(s)==1
pause(s)
else
pause(0)
end
k = k*3;
end