How generate an error to prevent an infinite loop in this function?

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Lorenz 2013-6-15

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https://ww2.mathworks.cn/matlabcentral/answers/79180-how-generate-an-error-to-prevent-an-infinite-loop-in-this-function

Hi, I'd like to know if it's possible to generate an error in this code(function) to prevent an infinite loop... I put an Initial matrix A of dimension 4x4. I want to make 8 groups by using this function (explanations below code):

    function [B, idx1, idx2] = selector(A)
    m=8;    %number of groups          
    n=numel(A);       
    ii=0;            
    idx=[];           
while ii<m 
    Permutation=randperm(n);
    id=setdiff(Permutation,idx,'stable');
  [ ii1,jj1]=ind2sub(size(A),id(1));
  [ ii2,jj2]=ind2sub(size(A),id(2)); 
   if or(abs(ii1-ii2)==1 & abs(jj1-jj2)==0,abs(ii1-ii2)==0 & abs(jj1-jj2)==1);
      ii=ii+1;                                       
      idx=[idx id(1:2)];                                                   
      B(ii,:)=[A(id(1)) A(id(2))];                                         
    end
end 
 disp(idx);
 [idx1,idx2]=ind2sub(size(A),idx);  
end

This function just returns groups (2 by 2) from elements of the matrix A. (these elements are adjacent (not diagonally) in A. And they're taken only one time) The matrix B contains these groups. (Just run the function to see) The function just run into an infinite loop when the last elements chosen in A are not adjacent and there are no other possibilities to group them. Thank You very much.

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Image Analyst 2013-6-15

What is A? Please give code to create a sample "A" and call selector(), so we can help you.

Lorenz 2013-6-16

在 MATLAB Online 中打开

ok sorry, A is a matrix dimension 4x4, A is that kind of matrix:

A =

   4     1     3
   2     3     1
   3     4     2
   1     2     4

We just apply the function to A. Example:

EDU>> [B ,idx1,idx2]=selector(A)
B =
       2     4
       3     1
       3     1
       2     4
       3     1
       1     3
       2     4
       4     2
idx1 =
       1     2     4     4     2     1     3     4     1     2     3     3     2     1     3     4
idx2 =
       1     1     1     2     3     3     4     4     4     4     1     2     2     2     3     3

This is how the function works. But sometimes, it can't make all the groups (just run the code to see), and I have to restart again and again till I have my 8 groups. This is what I want to correct. Thank you.

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