# Drawing a graph like the following

I want to try to draw a graph in TikZ like the following one For now, I have no idea how to approach without getting messy. Are there any helpful packages? Do I have to draw every line individually?

Thank you very much!

• You can start looking here: texample.net/tikz/examples – Sigur Nov 16 '18 at 19:35
• I did. But there was nothing helpful (at least I did not find anything). Especially when it goes to the surface with curved grid. – YoungMath Nov 16 '18 at 19:36
• Welcome to TeX.SE! You can do this easily with pgfplots or tikz-3dplot. – user121799 Nov 16 '18 at 19:37
• Do you have a minimal example for me? I need a concrete function, right? – YoungMath Nov 16 '18 at 19:46
• I guess the by far simplest possibility would be to compute the tangent analytically. Of course, you can also use this answer to draw the tangents. You may want to use the 3d library, since your plots live always in a plane. – user121799 Nov 16 '18 at 23:20

Yes, you need a function, and what is more write in such a way that others can read it. But this is even better, I have a perfect excuse not to punch in the texts. ;-) Maybe the following is a start.

\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{tikz-3dplot}
\begin{document}
\begin{tikzpicture}[font=\sffamily,declare function={%
f(\x,\y)=0.15*cos(\x*120)*cos(\y*120);}]
\tdplotsetmaincoords{70}{110}
\begin{scope}[tdplot_main_coords]
\draw[-latex] (0,0,0) -- (8,0,0) node[pos=1.1] {$x_1$};
\draw[-latex] (0,0,0) -- (0,8,0) node[pos=1.1] {$x_2$};
\draw[-latex] (0,0,0) -- (0,0,4) node[pos=1.1] {$x_3$};
\foreach \X in {1,...,5}
{
\draw plot[variable=\x,samples=51,smooth,domain=1:5] ({\X-f(\X,\x)},{\x+f(\X,\x)},{3});
\draw plot[variable=\x,samples=51,smooth,domain=1:5] ({\x-f(\X,\x)},{\X+f(\x,\X)},{3});
}
\draw[blue,thick] plot[variable=\x,samples=51,smooth,domain=1:5]
({3-f(3,\x)},{\x+f(3,\x)},{3});
\draw[red,thick] plot[variable=\x,samples=51,smooth,domain=1:5]
({\x-f(\x,3)},{3+f(\x,3)},{3}) ;
\draw[blue,thick] plot[variable=\x,samples=51,smooth,domain=1:5]
({3-f(3,\x)},{\x+f(3,\x)},{0});
\draw[red,thick] plot[variable=\x,samples=51,smooth,domain=1:5]
({\x-f(\x,3)},{3+f(\x,3)},{0}) ;
\end{scope}
\end{tikzpicture}
\end{document} EDIT: Motivated by @Sigur's comment, I slightly modified the setting such that now there are real projections. Let me stress that I really do not know what you want to plot as the other tikzlings have my crystal balls.

• Should the projections be straight lines? – Sigur Nov 16 '18 at 20:05
• @Sigur From the screen shot it is not clear they are projections. If they were, and if this function was used, then yes. But on the screen shot they are not straight, so I assumed these are not projections. – user121799 Nov 16 '18 at 21:01
• They are. It was badly sketched. I'm playing around. I will post the result soon. – YoungMath Nov 16 '18 at 22:18

After playing around a little bit, here's the result:

\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{tikz-3dplot}

\definecolor{darkolivegreen}{rgb}{0.33, 0.42, 0.18}

\begin{document}
\begin{tikzpicture}[font=\sffamily,declare function={%
f(\x,\y)=3+.075*cos(\x*100)*cos(\y*100)-.035*(\y-5)^2-.01*(\x-5)^2;
g(\x) = .075*(\x-4)^2+4;
h(\x) = .02*(\x-4)^3-.2*(\x-4)+4;
t(\x,\y)=f(4,4) -0.05*(\x-4) + 0.02*(\y-4); }]

\tdplotsetmaincoords{70}{110}

\begin{scope}[tdplot_main_coords]
\draw[-latex] (0,0,0) -- (8,0,0) node[anchor=north] {$x_1$};
\draw[-latex] (0,0,0) -- (0,8,0) node[anchor=west] {$x_2$};
\draw[-latex] (0,0,0) -- (0,0,4) node[anchor=south] {$z=u(x)$};

%Grid
\foreach \X in {1,...,6}
{
\draw[thin,gray] plot[variable=\x,samples=60,smooth,domain=1:6] ({\X},{\x},0);
\draw[thin,gray] plot[variable=\x,samples=60,smooth,domain=1:6] ({\x},{\X},0);
\draw[thin,gray] plot[variable=\x,samples=60,smooth,domain=1:6] ({\X},{\x},{f(\X,\x)});
\draw[thin,gray] plot[variable=\x,samples=60,smooth,domain=1:6] ({\x},{\X},{f(\x,\X)});
}

% Curves
\draw[darkolivegreen,thick] plot[variable=\x,samples=60,smooth,domain=1:6]
({g(\x)},{\x},{f(g(\x),\x)}) node [right] {\scriptsize $\varphi(S)$};

\draw[darkolivegreen,thick] plot[variable=\x,samples=60,smooth,domain=1:6]
({g(\x)},{\x},0) node [right] {\scriptsize $S$};

\draw[orange,thick] plot[variable=\x,samples=60,smooth,domain=1:6]
({\x},{h(\x)},0) node [below] {\scriptsize $x(t)$};

\draw[orange,thick] plot[variable=\x,samples=60,smooth,domain=1:6]
({\x},{h(\x)},{f(\x,h(\x))});

\node[orange, anchor=west] at ({0},{h(0)},{f(0,h(0))}) {\scriptsize $\begin{smallpmatrix} x(t) \\ v(t) \end{smallpmatrix}$};

% Tangent plane
\fill[purple!10,opacity=0.4,draw=purple] (3,3,{t(3,3)}) -- (3,5,{t(3,5)}) -- (5,5,{t(5,5)}) -- (5,3,{t(5,3)}) -- (3,3,{t(3,3)}) node[anchor=north west,purple,opacity=1] {\scriptsize $T_{\! x_0} \! \Gamma$};

% Vector fields
\draw[->,>=stealth,thick,blue] (4,4,{f(4,4)}) -- (3.95,4.02,2) node [below] {\scriptsize $N(x_0)$};
\draw[->,>=stealth,red,thick] (4,4,0) -- (3,4.2,0) node[anchor=west] {};
\draw[->,>=stealth,red,thick] (4,4,{f(4,4)}) -- (3,4.2,{f(4,4)+.06}) node[anchor=south east] {};

% Points
\fill[black] (4,4,0) circle (1pt) node[anchor=north] {\scriptsize $x_0$};
\fill[black] (4,4,{f(4,4)}) circle (1pt) node[anchor=north east] {};
\end{scope}
\end{tikzpicture}
\end{document} What do you think? Any further suggestions or improvements? I computed the slopes manually and defined the tangent plane as a function.