= Positive-semidefinite-plus-nonnegative cone
{title2=$\mathbb S_+^n+\mathbb N^n$}
The sums $P+N$ of a real <positive semidefinite matrix> $P$ and a symmetric <nonnegative matrix> $N$ form a <convex cone> inside the <copositive cone>. Both terms have nonnegative <quadratic forms> on the <nonnegative orthant>. The <Horn copositive matrix> shows that the inclusion is strict in dimension five; the <sum of squares criterion for a biquadratic form> explains this cone's relation to <semidefinite programming>.
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