## Making a labeled Klein bottle using TikZ or pgfplots?

I'd like to be able to draw the following cell complex structure on the (three-dimensional embedding of the) Klein bottle using LaTeX. I am pretty pleased with my hand-drawn rendition, but LaTeX is prettier, and can be edited. I am still in the process of learning TikZ, and I have not used the pgfplots package before, so I don't know if it can help. The only places I found online that seemed related wereKlein bottlepgfplots in combination with gnuplot requires additional semicolon Edit: Thanks to hpesoj626's helpful comment below, I have got gnuplots working, so I can compile at least the second example above now (I still don't know how to implement the first one). However, there is still the issue of decorating the Klein bottle with the various curves and points I want to draw, which neither post addresses. Also, both plotting solutions seem to be too "heavy", visually, to really make labeling them in the way I want seem viable. I am looking for more of an outline-looking Klein bottle. If the ultimate answer is that I need to draw it out "by hand" (i.e. plan out a 2-dimensional image representing the Klein bottle), then please post any advice you have about how to go about doing that. Can anyone suggest a method of drawing this in LaTeX?

## Solutions/Answers:

### Answer 1:

Further explanations will follow, for now so much:

- put your sketch in a node
- recreate the lines using draw commands (I used
`to[in=,out=,looseness=]`

) - remove the sketch

It’s far from perfect, somee labels are missing. You can increase the quality ba adding more intermediate points.

## (Final) Code

```
\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{tikz}
\usetikzlibrary{scopes,intersections}
\newcommand{\Coordinate}[2]%
{ \coordinate (#1) at (#2);
%\fill[red] (#2) circle (0.05) node[above] {#1};
}
\begin{document}
\begin{frame}
\begin{tikzpicture}
% \node[above right,inner sep=0,outer sep=0] (a) {\includegraphics{klein.png}};
% \draw[orange,thin,dashed,] (a.south west) grid (a.north east);
% \foreach \x in {0,...,10}{\node [below] at (\x,0) {\x};}
% \foreach \y in {0,...,12}{\node [left] at (0,\y) {\y};}
\node[fill=blue,circle,label=0:P1,inner sep=0.5mm] (P1) at (4.9,6.7) {};
\node[fill=blue,circle,label=270:P2,inner sep=0.5mm] (P2) at (2.5,5.4) {};
\node[fill=blue,circle,label=45:P3,inner sep=0.5mm] (P3) at (1.6,4) {};
\Coordinate{e5b}{3.6,1.3}
\Coordinate{e4l}{0.7,4.8}
\Coordinate{e4r}{9.9,3.7}
\Coordinate{si}{4.5,7.4}
\Coordinate{bottom}{6.8,0.9}
{[very thick,black]
\draw (e4l) to[out=270,in=160,looseness=1] (P3);
\draw (P3) to[out=340,in=270,looseness=0.3] node[above,pos=0.7,black] {$e_4$} (e4r);
\draw[name path=P2e4r] (P2) to[out=120,in=80,looseness=3.7] node[below left,pos=0.7,black] {$f_2$} (e4r);
\draw[name path=P1P1] (P1) to[out=160,in=270,looseness=1] (2.6,9) to[out=90,in=90,looseness=1.3] node[above, pos=0.5,black] {$e_3$} (6.6,9.6) to[out=270,in=40,looseness=1] (P1) ;
\draw (P2) to[out=315,in=315,looseness=0.5] node[below right,pos=0.5,black] {$e_1$} (P1);
\draw[dashed] (P2) to[out=135,in=135,looseness=0.5] node[below right,pos=0.5,black] {$f_1$} (P1);
\draw (P2) to[out=220,in=90,looseness=1] (P3);
\draw (P3) to[out=270,in=150,looseness=1] (e5b);
\draw (e4l) to[out=270,in=160,looseness=1.3] (e5b);
\draw (e5b) to[out=340,in=260,looseness=1.1] (e4r);
\draw[dashed] (P2) to[out=300,in=330,looseness=1] (e5b);
\draw[dashed] (e4l) to[out=90,in=90,looseness=0.6] (e4r);
\draw[dashed] (P1) to[out=320,in=190,looseness=0.4] (bottom);
\draw (P1) to[out=110,in=300,looseness=1] (si);
\draw (si) to[out=120,in=270,looseness=1] (4,8.5) to[out=90,in=180,looseness=1] (5.2,9.7) to[out=0,in=90,looseness=1] (6,9) to[out=270,in=20,looseness=1] (si);
\path[name path=e4lsi] (e4l) to[out=90,in=200,looseness=0.8] (si);
\draw[name intersections={of=e4lsi and P2e4r}] (e4l) to[out=90,in=210,looseness=1] (intersection-1) coordinate (h1);
\draw[dashed] (intersection-1) to[out=30,in=200,looseness=0.6] (si);
}
\end{tikzpicture}
\end{frame}
\end{document}
```

## Output

### Answer 2:

Here’s an alternative to Tom Bombadil’s which uses the Hobby algorithm for generating a smooth path through a given set of points (see Curve through a sequence of points with Metapost and TikZ). The point of using this is that it makes it easier to draw an ill-defined shape as you just keep specifying more points on it until it “looks right” – there’s no mucking about with looseness or similar. I think that the resulting code looks cleaner as well.

```
\documentclass{article}
%\url{https://tex.stackexchange.com/q/77606/86}
\usepackage{tikz}
\usetikzlibrary{hobby}
\begin{document}
\begin{tikzpicture}[use Hobby shortcut]
\draw ([closed,blank=soft]0,0)
\foreach \pt in {
(-2,2),
(2,2),
(2,-2),
(-2,-2),
([blank]-2,-1),
(-1,-1),
(1,-2),
([blank=soft]1,2),
([blank=soft]-1,1),
(-3,3),
(6,4.5),
(4.5,-4.5),
(-2.5,-6)
} {
.. ++\pt
};
\draw[dashed,use previous hobby path={invert soft blanks}];
\draw (0,0) .. +(-1,-1) .. ++(-2,-1);
\draw[dashed] (0,0) .. +(-1,-.75) .. ++(-2,-1);
\draw (-2.45,-3.9) .. +(3.3,-.75) .. (4.2,-3.95);
\draw[dashed] (-2.45,-3.9) .. +(4.3,.5) .. (4.2,-3.95);
\end{tikzpicture}
\end{document}
```

Result:

Note that we actually draw the path twice, but invert (mostly) which parts are blanked (this wouldn’t be possible via a postaction as it involves modifying the actual path; but when the algorithm is run then it merely generates the points so we can reuse that list but specify different actions to take). This makes it possible to use the same specification and draw the inside and outside parts differently. I mean the *outside* and *inside* parts differently. That is to say, the *inside* and … oh, never mind.

You have to get the latest version of the hobby code (`hobby.dtx`

, then run `tex hobby.dtx`

) from the TeX-SX launchpad project as I added a few features to make this work.

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