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Averaging over a symmetric matrix

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MiauMiau on 14 Aug 2017
Commented: MiauMiau on 14 Aug 2017
Given an m,n matrix, I want to create a new matrix by doing the following: The element (i,d) and the element (d,i) should be averaged, the diagonal elements can be ignored. So for instance we average over element (1,5) and (5,1) which gives us a new (single entry) and hence a smaller matrix at the end - how can that be done in a quick way (not too many loops)?

Accepted Answer

Guillaume on 14 Aug 2017
Edited: Guillaume on 14 Aug 2017
I don't see how you get a smaller matrix but doing the averaging is trivial:
(yourmatrix + yourmatrix.') / 2
You can triu or tril that result to keep the upper or lower triangle since it's symmetric.
And of course, it only works with square matrix otherwise there won't always be an (i,d) for a (d,i)

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