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I'm reading one paper and on page 36 (48 in the pdf) it says:"

Let d(s, i) be the (positive) diagonal terms that need to be subtracted from the matrix to make it negative semi-definite..." semi-definite...

Could someone explain me why it's possible and how can I get the values of these terms?

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Subtract diagonal terms from the matrix to make it negative semi-definite

I'm reading one paper: "Let d(s, i) be the (positive) diagonal terms that need to be subtracted from the matrix to make it negative semi-definite..."

Could someone explain me why it's possible and how can I get the values of these terms?