rainbow” post=91160Sì, voglio esattamente lo stesso disegno dell’immagine, ma non so come rappresentarlo.
`\documentclass
{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\draw [-latex] (0,0) — (-2.4,-2.3) node [below right] {$x$};
\draw [-latex] (0,0) — (4.2,-1.3) node [below] {$y$};
\draw [-latex] (0,0) — (0,2.2) node
{$z$};
\draw (0,0.4) .. controls (1.4,0.6) and (0.1,-1.7) .. (2,-2.45)
to [bend left=18, relative] (4.8,0.5) node [above right] {$z=f(x,y)$}
.. controls (3.5,0.7) and (3.4,1.8) .. (2.6,2.15)
to [bend right=26, relative] cycle;
\draw [dash dot] (2.4,1.4) — (2.4,-2.8);
\fill (2.4,1.4) circle [radius=1pt]
(2.4,-2.8) circle [radius=1pt] node [below right] {$(x,y)$};
\draw (1.45,2.1) — (2.15,0) — (3.8,0.7) — (3,2.7) — cycle;
\end{tikzpicture}
\end{document}`
[attachment=887]prova1_2014-01-17.png[/attachment]