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
Image Analyst
Image Analyst on 12 Apr 2014
You're welcome. Can you mark the answer as "Accepted" then?

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