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moving averege of a matrix

Asked by Rica

Rica

on 6 Mar 2013
Accepted Answer by Andrei Bobrov

Andrei Bobrov

Hi!

a have a matrix:

%
A=[2 5 6 8 7 ;2 2 3 5 6; 1 2 3 4 2]

how could i calculate the moving averege (order 2) of the matrix horizentally, i mea the vectors a1= [2 5 6 8 7] and a2=[2 2 3 5 6] a3=[1 2 3 4 2] are indepandent .

the moving averege of each vector?

thank you

0 Comments

Rica

Rica

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3 Answers

Answer by Andrei Bobrov

Andrei Bobrov

on 6 Mar 2013
Accepted answer
out = conv2(A,[.5 .5],'same');
out(:,1:end-1);

2 Comments

Andrei Bobrov

Andrei Bobrov

on 6 Mar 2013
out = [A(:,1),conv2(A,[.5 .5],'valid')];
Daniel

Daniel

on 6 Mar 2013

For an A of 1e3 x 1e5, it appears that Jan's direct method is faster, but if you are not worried about the edge, then your method is faster.

Andrei Bobrov

Andrei Bobrov

Answer by Jan Simon

Jan Simon

on 6 Mar 2013
Edited by Jan Simon

Jan Simon

on 7 Mar 2013
A = [2 5 6 8 7 ;2 2 3 5 6; 1 2 3 4 2];
B = (A(:, 1:4) + A(:, 2:5)) * 0.5;

This is one column shorter than the input, but how is the moving average defined at the edges?

[EDITED] A hard coded moving average for 5 neighboring elements along the rows:

[d1, d2] = size(X);
Z1 = zeros(d1, 1);
Z2 = zeros(d1, 2);
M = X + [Z1, X(:, 1:d1 - 2) + X(:, 3:d1), Z1] + ...
        [Z2, X(:, 1:d1 - 4) + X(:, 5:d1), Z2];
divV(1, [1, 2, d1 - 1, d1]) = [1, 3, 3, 1];
divV(1, 3:d1 - 2) = 5;
Y = bsxfun(@rdivide, M, div);

Here the first element is not changed and the 2nd is the average of the elements 1 to 3. I do not assume that this can beat CONV.

3 Comments

Rica

Rica

on 6 Mar 2013

the matrix to be avereged is too big!!

the first value stay unchanged.

thank you

Jan Simon

Jan Simon

on 6 Mar 2013

Too big for what? Why is the first value unchanged and what exactly is "the first value"?

Rica

Rica

on 7 Mar 2013

my matrix is of the size 27*301528. i want the moving averege of each raw. the size of zhe window should be 5. that means or the first 5 value , i build the mean value with the mean function. from the sixth value should the moving averege start.

i am tryin now to use filter2, but i will be happy for other advices.

thank you

Jan Simon

Jan Simon

Answer by Image Analyst

Image Analyst

on 6 Mar 2013

Moving how? In an m by n window? Or do you simply want the average of the entire row, in which case you can do this:

rowAverages = mean(A, 2);

1 Comment

Image Analyst

Image Analyst

on 7 Mar 2013

Rica, if you want the mean of 5 horizontal numbers in a 27 by 302,528 matrix, you can do this:

means = conv2(yourArray, [1 1 1 1 1]/5, 'valid');
Image Analyst

Image Analyst

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