Asked by Rica
on 22 Mar 2013

hi!
I want to use the **filter** function as a moving averege filter. the Type of the filter should be IIR Filter. Te window length is 3.
for exemple:

% X=rand(1:300) B=1/3 A=1-B; Y=filter(B,A,X)->First order IIR filter

the filter functi should start after reaching the window lenght. for the first 2 value (before reaching the window lenght of 3) , i wan to calculate just the mean value.

% Y(1)=X(1) Y(2)=mean(Y(1)+X(2)); Y(3:end)=filter(B,A,X(3:end))

could someone help me ?

thank you

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Answer by Andrei Bobrov
on 22 Mar 2013

Edited by Andrei Bobrov
on 22 Mar 2013

Accepted answer

EDIT

out = filter([1 1 1]/3, 1, x(:)); out(1:2) = [x(1);sum(x(1:2))/2];

Answer by Image Analyst
on 22 Mar 2013

Edited by Image Analyst
on 22 Mar 2013

To get the middle chunk, do this:

yMiddle = conv(x, [1 1 1]/3, 'valid');

Then prepend and append the endpoints as you already calculated.

**Edit:**
Haven't heard from you, so here's a full-blown demo for you. It shrinks the window as it gets closer to the edges. Let me know if you need a version robust enough to handle any window size.

x = 1:10 % Get the first and last elements. yFirst = mean(x(1:2)) yLast = mean(x(end-1:end)) % Now get the middle with a moving average. yMiddle = conv(x, [1 1 1]/3, 'valid') yFinal = [yFirst yMiddle, yLast]

In the command window you see:

x = 1 2 3 4 5 6 7 8 9 10 yFirst = 1.5000 yLast = 9.5000 yMiddle = 2.0000 3.0000 4.0000 5.0000 6.0000 7.0000 8.0000 9.0000 yFinal = 1.5000 2.0000 3.0000 4.0000 5.0000 6.0000 7.0000 8.0000 9.0000 9.5000

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