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What are all the matrices that commute wit a matrix of ones?

  1. Mar 2, 2013 #1
    1. The problem statement, all variables and given/known data

    What are the characteristics of a matrix that commutes with a matrix of ones?

    2. Relevant equations

    None.

    3. The attempt at a solution

    I'm helping a buddy with his homework and I can't figure out this problem.
     
  2. jcsd
  3. Mar 2, 2013 #2

    jbunniii

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    Try working it out explicitly for a 2x2 matrix (it's easy) and see if you can generalize from there.
     
  4. Mar 2, 2013 #3

    Simon Bridge

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    What about the definition of "commute"?
     
  5. Mar 3, 2013 #4
    Figured out the answer, I think. The sum of every row and column is the same.
     
  6. Mar 4, 2013 #5

    Dick

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    Sounds right, can you prove it?
     
  7. Mar 4, 2013 #6
    Yes, but the problem doesn't ask me to
     
  8. Mar 4, 2013 #7

    Dick

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    Fair enough.
     
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