= Interior of the copositive cone
{title2=$\operatorname{int}\operatorname{COP}_n$}
The <interior> consists exactly of <strictly copositive matrices>. If $x^TAx$ has positive minimum $\delta$ on the <compact> nonnegative <unit sphere>, perturbations of <operator norm> less than $\delta$ preserve this positive lower bound there. Conversely, if a unit nonnegative <vector> has zero <quadratic form>, $A-\varepsilon I$ leaves the <copositive cone> for every $\varepsilon>0$. Thus such a <matrix> is not <interior>. The <identity matrix> is a convenient <interior> point.
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