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POHow to check a matrix is/isn't in an array (Matlab)
 

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  1. POHow to check a matrix is/isn't in an array (Matlab)
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    <p>I have an array (M) of matrices. I perform an operation on the matrix in the ith position, and it adds three more matrices to my array in the (3i-1), (3i) and (3i+1)th positions. I want to continue this process until I reach the jth position in the array, where j is such that all matrices in the (j+1)th position and onwards have appeared already somewhere between positions 1 and j (inclusive).</p> <p>EDIT: I've been asked to clarify what I mean. I am unable to write code that makes my algorithm terminate when I want it to as explained above. If I knew a proper way of searching through an array of matrices to check if a given matrix is contained, then I could do it. I tried the following:</p> <pre><code>done = 0; ii = 1 while done ~= 1 %operation on matrix in ith position omitted, but this is where it goes for jj = ii+1:numel(M) for kk = 1:ii if M{jj} == M{kk}; done = done + 1/(numel(M) - ii); break end end end if done ~= 1 done = 0; end ii = ii + 1 end </code></pre> <p>The problem I have with this (as I'm sure you can see) is that if the process goes on for too long, rounding errors stop ever allowing done = 1, and the algorithm doesn't terminate. I tried getting round this by introducing thresholds, something like</p> <pre><code>while abs(done - 1) &gt; thresh </code></pre> <p>and </p> <pre><code>if abs(done - 1) &gt; thresh done = 0; end </code></pre> <p>This makes the algorithm work more often, but I don't have a 'one size fits all' threshold that I could use (the process could continue for arbitrarily many steps), so it still ends up breaking.</p> <p>What can I do to fix this?</p> <p>Thanks</p>
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    1. USMatt Lab
    1. USMatt Lab
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    1. COI don't quite see how the content of the the question relates to the question title. What is it you're asking please? Also, can you provide `M` to make your code properly reproducible. Finally, if you have nested loops like that in MATLAB, it usually means you are doing something wrong. I suggest you clarify your real objective so we can find a better way of writing your code.
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      1. POHow to check a matrix is/isn't in an array (Matlab)
      1. USRichie Cotton
    2. COThanks for your response. I've edited my post now to make my question clearer; I think you'll find it does relate to the title. I fail to see what you mean by "wrong". My aim is to write an algorithm that gives me the output I want it to in an acceptable amount of time. I'm new to programming, but most other algorithms I have written use nested loops and work perfectly well.
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      1. POHow to check a matrix is/isn't in an array (Matlab)
      1. USMatt Lab
    3. COI too don't see how the title correlates with what you're asking. It would be better if you change it to something more relevant such as "loop not terminating correctly" or something. It will also help you since interested people will actually read your true question based on the title.
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      1. POHow to check a matrix is/isn't in an array (Matlab)
      1. USJorge
 

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