Filtering code- unknown filter

Hi to all,

I have a code which filters the signal 'x' with length of N, but I don't know what kind of filtering that is? The code is:

%Filtering.
  fL=5; % Setting fL
  if fL>1
      for i=fL+1:N
          x(i-fL)=0;
          for j=1:fL
              x(i-fL) = x(i-fL)+(1/fL)*x(i-j+1);
          end
      end
  end

Can you help me to know that? thanks,

[Azzi Abdelmalek]

you should specify what is N?

[Coo Boo]

N stands for the length of signal

Answer 1

[Matt Fig]

It is a forward moving average. That is, the value at index I is the average of the fL values I+1:I+fL. Like other moving averages, it can be considered a low-pass filter.

Here is a simplification of the code that makes this more clear:

y = x;  % Compare final x with final y after both loops.
for jj = 1:length(y)-fL
   y(jj) = sum(y(jj+1:jj+fL)/fL) 
end

What is interesting is that it stops short of carrying to the end of the vector. Most moving averages carry through with less terms as necessary, like this:

for jj = 1:length(y)-1
   y(jj) = sum(y(jj+1:min(jj+fL,length(y)))/fL) ;
end

Also y above to compare:

MA = fliplr(filter(ones(1,5)/5,1,fliplr(y)));

only the first and the last elements differ because of the way MAs work.

[Coo Boo]

Thanks

Answer 2

[Azzi Abdelmalek]

 x=rand(104,1);y=x
 N=size(x,1);
 fL=5; % Setting fL
  if fL>1
      for i=fL+1:N
          x(i-fL)=0;
          for j=1:fL
              x(i-fL) = x(i-fL)+(1/fL)*x(i-j+1);
          end
      end
    end
    cla;plot(abs(fft(x)));hold on ;plot(abs(fft(y)),'r')

it seems to be a low pass filter, comparing the Fourier transform of x and y

your original: red

your filtred signal: blue

[Coo Boo]

Thanks for your help and answer. But I want to know its exact name, if it has. Thanks again

[Azzi Abdelmalek]

just look at the half of the plot (from 0 to 52), because froù 53 to 104 it's just a symetric

[Coo Boo]

I think, this will show better for bigger value of fL,e.g. fL=20

plot(abs(fft(x(1:N-fL))));hold on ;plot(abs(fft(y)),'r')