Matrix addition and means

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Joseph Pauwels
Joseph Pauwels on 11 Apr 2014
Commented: Image Analyst on 12 Apr 2014
I am trying to take a matrix of any size , whether it has one row or 9, and write a function file that add the each element by its immediate neighbor then average it and replace. So if
a=[1,2,0,1]
the function would produce
ans =
1.5 1 1 .5
here is what I have so far, but for some reason it wont add the edges.
function [ b] = Avg_Num(a )
%UNTITLED Summary of this function goes here
% Detailed explanation goes here
[r,c]=size(a);
if (r*c) == 1
b=a;
elseif r ==1
b(1,1)=(a(1,1)+a(1,2))/2;
for j= 2:(c-1)
b(1,j)=(a(1,j)+a(1,j-1)+a(1,j+1))/3;
b(1,max(j)+1)=(a(1,max(j))+a(1,max(j)+1))/2;
end
elseif r >1
b(1,1)=(a(1,1)+a(1,2)+a(2,2)+a(2,1))/4;
b(1,c)=(a(1,c)+a(1,c-1)+a(2,c)+a(2,c-1))/4;
b(r,1)=(a(r,1)+a(r-1,1)+a(r,2)+a(r-1,2))/4;
b(r,c)=(a(r,c)+a(r-1,c)+a(r-1,c-1)+a(r,c-1))/4;
for i=2 :(r-1)
for j=2:(c-1)
b(i,j)=(a(i,j)+a(i+1,j)+a(i-1,j)+a(i,j+1)+a(i,j-1)+a(i-1,j-1)+a(i-1,j+1)+a(i+1,j-1)+a(i+1,j+1))/9;
end
end
end
end
any ideas
  1 Comment
Azzi Abdelmalek
Azzi Abdelmalek on 11 Apr 2014
How did you get the result from a=[1,2,0,1] ?

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Answers (1)

Image Analyst
Image Analyst on 11 Apr 2014
Edited: Image Analyst on 11 Apr 2014
Wow. How would you like to do all that in a single line? If so, how about using convolution:
% First with a 1D "a"
a=[1,2,0,1];
output = conv2(a, [1, 1]/2, 'same')
% Now with a 2D "a" - use a 3 by 3 array to do the scanning.
windowSize = 3
a = magic(windowSize); % Sample data
output = conv2(a, [windowSize, windowSize]/windowSize^2, 'same')
  12 Comments
Joseph Pauwels
Joseph Pauwels on 12 Apr 2014
thats amazing, and it works on any size vector. my hat goes off to you.
Thanks for your help
Image Analyst
Image Analyst on 12 Apr 2014
You're welcome. Can you mark the answer as "Accepted" then?

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