# Graph of a set homeomorphic

I would like to please guide me on this question: Let $S_+$ denote the set of semi positive definite matrices in $\mathbb{R}^{2\times 2}$ is known that $S_+\subseteq Sym \simeq\mathbb{R}^{3}$,wherein $Sym$ are the matrices symmetric. But Is it possible to give a geometric interpretation of $S_+$ in $\mathbb{R}^{3}$? Can be graphed? Thank you very much for your attention, any suggestions are welcome.

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