# for loop summation problem

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Abbass Ibrahim on 10 Jun 2022
Answered: Mathieu NOE on 10 Jun 2022
i want to add my signals in a for loop , i want to add my values in a for loop so that the a(i)=a(i-1)+b(i)

Mathieu NOE on 10 Jun 2022
hello
please clarify what is a and b in your request. Usually those letters are used for numerator (B) and denominator (A) of an IIR digital filter.
see example below : a and b are coefficients of IIR filter (fixed), x is the input data and y is the output
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% data
[samples,channels] = size(x);
dt = 1/Fs;
time = (0:samples-1)*dt;
%% IIR filter recursive equation
c1 = 8;
c2 = 2;
c3 = 7;
b0 = 0.05 * c1;
b1 = 0.03 * c2;
b2 = 0.02 * c3;
a1 = 0.5;
a2 = 0.5;
% manual for loop coding IIR filter
y(1) = b0*x(1) + 0 + 0 + 0 + 0; % 1st iteration
y(2) = b0*x(2) + b1*x(1) + 0 + a1*y(1) + 0; % 2nd iteration
for k = 3:samples % for iteration # 3 and after
y(k) = b0*x(k) + b1*x(k-1) + b2*x(k-2) + a1*y(k-1) + a2*y(k-2);
end
figure(1)
plot(time,x,time,y)

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