Challenging Question - Finding mean of specific values of matrix and re-entering

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Karan 2014-8-27

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评论： Image Analyst 2014-8-28

Have tried countless times but need help

Writing script which has matrix M and returns a new Matrix where each element of N is the corresponding element of M averaged with its next elements above, below and left and right.

The script must work for any sized square matrix!

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Answer 1

Arnaud 2014-8-27

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Fonctionne pour n'importe quel noyau K de taille 3 (facile à passer à une taille quelconque) et matrice M de taille quelconque :

M = [1 2 3; 4 5 6; 7 7 9];
K = [0 1 0;1 1 1;0 1 0];
Y = conv2(padarray(M,[1 1]),K,'same');
OK = conv2(padarray(ones(size(M)),[1 1]),K,'same');
Y = Y(2:end-1,2:end-1)./OK(2:end-1,2:end-1)

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Andrei Bobrov 2014-8-27

+1

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Answer 2

Salaheddin Hosseinzadeh 2014-8-27

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Hey Karan,

Sound very easy and typical!

It's nothing but programming and defining some conditions. you need 2 for loops for 2 dimension matrix, one to check for vertical neighbors and one for horizontal neighbors.

Once you're finding the neighbors in for loops you should check not to exceed matrix x or y dimension, and also not getting below 1, there is no index 0 in matlab (C C++ has index 0)

and neighbor definition is the current index - and + 1 as you know.

Find them correctly, add them and put them in a new matrix using the current index.

Oh, BTW, to get the matrix dimension you can use size

size(M,1) or size(M,2) whichever you need!

see MATLAB documentation for size

doc size

Good Luck!

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Answer 3

Andrei Bobrov 2014-8-27

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编辑：Andrei Bobrov 2014-8-27

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s = size(M);
l = true(s);
l(2:end-1,2:end-1) = false;
l1([1,s(1),numel(M)-[s(1)-1,0]]) = true;
l1 = reshape(l1,s);
l2 = l & ~l1;
N = conv2(M,[0 1 0;1 1 1;0 1 0]/5,'same'); % N = imfilter(M,[0 1 0;1 1 1;0 1 0]/5);
N(l1) = N(l1)*5/3;
N(l2) = N(l2)*5/4;

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Answer 4

stalin 2014-8-27

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编辑：Randy Souza 2014-8-28

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clear all
A=[1 2 3 4;5 6 7 8; 9 10 11 12; 13 14 15 16]
[l m]=size(A)
for i=1:l
    for j=1:m
        if i==1&&j==1
            B(i,j)=(A(i,j)+A(i+1,j)+A(i,j+1))/3
        elseif i==1&&j==m
            B(i,j)=(A(i,j)+A(i+1,j)+A(i,j-1))/3
        elseif i==l&&j==1
            B(i,j)=(A(i,j)+A(i-1,j)+A(i,j+1))/3
        elseif i==l&&j==m
            B(i,j)=(A(i,j)+A(i-1,j)+A(i,j-1))/3
        elseif i==1
            B(i,j)=(A(i,j)+A(i+1,j)+A(i,j-1)+A(i,j+1))/4
        elseif i==l
            B(i,j)=(A(i,j)+A(i,j+1)+A(i,j-1)+A(i-1,j))/4
        elseif j==1
            B(i,j)=(A(i,j)+A(i-1,j)+A(i+1,j)+A(i,j+1))/4
        elseif j==m
            B(i,j)=(A(i,j)+A(i+1,j)+A(i-1,j)+A(i,j-1))/4
        else
%             B(i,j)=0
           B(i,j)= (A(i,j)+A(i-1,j)+A(i,j+1)+A(i+1,j)+A(i,j-1))/5
        end
    end
end