Storing the positions of neighbouring elements that have specific values.

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Phillip Smith 2019-11-27

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https://ww2.mathworks.cn/matlabcentral/answers/493489-storing-the-positions-of-neighbouring-elements-that-have-specific-values

评论： Phillip Smith 2019-11-27

A = zeros(5,5);
A(3,4)=1;
A(4,1)=1

I have a matrix of zeros with two 1's in postions (3,4) and (4,1). Starting with the 1 at (3,4) I want to store all the positions of neighbouring elements that are eqaul to 0. I want to do this as my next step is to choose one of the neighbours that equal 0, change that to a 1, and then start the whole process again, starting at any element that equals 1.

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Answer 1

dpb 2019-11-27

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https://ww2.mathworks.cn/matlabcentral/answers/493489-storing-the-positions-of-neighbouring-elements-that-have-specific-values#answer_403612

在 MATLAB Online 中打开

>> i0=3; j0=4;
>> [i,j]=find(~A(i0-1:i0+1,j0-1:j0+1));
>> [i,j]
ans =
          1.00          1.00
          2.00          1.00
          3.00          1.00
          1.00          2.00
          3.00          2.00
          1.00          3.00
          2.00          3.00
          3.00          3.00
>> 

You'll have to restrict search to either include only interior initial points or modify to account for location on boundary in computing range vectors.

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dpb 2019-11-27

编辑：dpb 2019-11-27

在 MATLAB Online 中打开

Just add the initial position offset less one for one-based counting (twice)...

>> [i+i0,j+j0]-2
ans =
          2.00          3.00
          3.00          3.00
          4.00          3.00
          2.00          4.00
          4.00          4.00
          2.00          5.00
          3.00          5.00
          4.00          5.00
>> 

Phillip Smith 2019-11-27

在 MATLAB Online 中打开

I did this and has worked perfectly

[r,c]=find(~D(i:i+2,j:j+2));
          E=[r,c];
          n=length(E);
          for k=1:n
              for x=1:2
                  if E(k,x)==1
                     E(k,x)=-1;
                  elseif E(k,x)==2
                     E(k,x)=0;
                  elseif E(k,x)==3
                     E(k,x)=+1;
                  end
                  
              end
          end
          Y= E+[i j]; 
          