Matrix addition and means

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Joseph Pauwels 2014-4-11

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https://ww2.mathworks.cn/matlabcentral/answers/125396-matrix-addition-and-means

评论： Image Analyst 2014-4-12

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

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Azzi Abdelmalek 2014-4-11

How did you get the result from a=[1,2,0,1] ?

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回答（1 个）

Image Analyst 2014-4-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/125396-matrix-addition-and-means#answer_133037

编辑：Image Analyst 2014-4-11

在 MATLAB Online 中打开

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')

Window size is how big you want the window to be. Like 9. It's usually an odd number because you want the output element to be at the center of the window. But it doesn't have to be, you'll just have a half-element shift otherwise.

'same' means that the window travels over the entire array and quits if the scanning widow is not centered over the last element. For example, what if the array was 10 wide and your window was 7 wide. When the center element of the window (#4) is over the last element of your array (#10), it quits. If you use 'valid, it quits when the scanning window's outer edge hits the outer edge of the array its scanning. If it's full, it will go until there are no more overlapping elements. For example the last over lap at 10, when the scanning kernel goes from element 10 to 16, but only the elements at 10 are overlapped. The elements under the kernel that are not part of the original array are assumed to be zero when it does the multiply and add. You need to know how you want to handle it when you have these situations, called "edge effects" or "boundary effects".

Joseph Pauwels 2014-4-12

thats amazing, and it works on any size vector. my hat goes off to you.

Thanks for your help

Image Analyst 2014-4-12

You're welcome. Can you mark the answer as "Accepted" then?

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MATLAB Language Fundamentals Matrices and Arrays Matrix Indexing

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