Hi Saleh,
This can be done through for loop. The documentation link to for loop is https://www.mathworks.com/help/matlab/ref/for.html. Please go through this to have easy going.
The code for what is asked is: (There is no intimation of k in the condition)
% Consider a random signal of length N
N = 100;
r = rand(N,1);
% Smoothing factor a
a = 10;
% Write the loop
tmp = 0;
w = zeros(N,1);
for j = 1:N
w(j) = a*tmp+ (1-a)*r(j);
tmp = w(j);
end
% The output is provided in w
w
Hope this helps.
Regards,
Sriram
