[Math] Diagonal dominance versus positive semi-definiteness

linear algebramatricespositive-semidefinite

I know that for a symmetric matrix $A$, diagonal dominance, i.e. $$A_{ii} \ge \sum\limits_{j \ne i} |A_{ij}|$$ implies positive semi-definiteness.

How about the other way? Does positive semi-definiteness imply diagonal dominance? Could you point to a proof or a counter example?

Best Answer

Quick counter example

>>> a=2*ones(3,3)+eye(3)
a =

   3   2   2
   2   3   2
   2   2   3

>>> eig(a)
ans =

   1.00000
   1.00000
   7.00000
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