<p>Mesh drawing of a closed surface, given by the equation:
</p>
<dl><dd><dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle z=-x^{2}-y^{2}\,}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mi>z</mi><mo>=</mo><mo>−<!-- − --></mo><msup><mi>x</mi><mrow class="MJX-TeXAtom-ORD"><mn>2</mn></mrow></msup><mo>−<!-- − --></mo><msup><mi>y</mi><mrow class="MJX-TeXAtom-ORD"><mn>2</mn></mrow></msup><mspace width="thinmathspace"></mspace></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle z=-x^{2}-y^{2}\,}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4c7b7e7f72f9a956ba9d655fdafcbe452de723f4" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.671ex; width:13.821ex; height:3.009ex;" alt="{\displaystyle z=-x^{2}-y^{2}\,}"></span></dd></dl></dd></dl>
This was plotted in Mathematica and traced using Inkscape to give a smoother result. The Mathematica code is given below. This drawing is one in a series.
<a href="//commons.wikimedia.org/wiki/User:Inductiveload" title="User:Inductiveload">Inductiveload</a>
Own drawing, Inkscape 0.45