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This matrix has only '1's on its main diagonal:

$A = \begin{pmatrix} 1 & 0 & 0 & 0\\ 0 & 1 & 0 & 0\\ 0 & 0 & 1 & 0\\ 0 & 0 & 0 & 1 \end{pmatrix}$

But whats the opposite of main diagonal?

I want to say something like: "There are only '0's on the NOT-main-diagonal"

Can someone help me with a word?

hardfork
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    "not-main-diagonal" can mean either "not-(main-diagonal)" (i.e. the entries which are not on the main diagonal), or "(not-main)-diagonal" (i.e. the diagonal which goes from top right to bottom left, and therefore is not the main diagonal). I think you mean the first one, and the answer below is correct in that case. But just to be sure: which one do you mean? – Arthur May 27 '18 at 07:51
  • yes, the first. – hardfork May 27 '18 at 07:57

1 Answers1

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They are known as off-diagonal elements.

Check out the Wikipedia links:

KingLogic
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