# TikZ: Curve through specified points

\documentclass{standalone}
\usepackage{comment}

\usepackage{tikz,pgf}

\usetikzlibrary{fit,scopes,calc,matrix,positioning,decorations.pathmorphing}

\begin{document}

\begin{tikzpicture}
\begin{scope}
\matrix (A5) [matrix of nodes, ampersand replacement = \&] {
{7}  \& {2} \& {7} \& {7} \& {2} \& {8}\\
};
\end{scope}
\begin{scope}
\matrix (B5) at ([yshift=-2.5cm]A5-1-1.south) [anchor=B5-1-1.north, matrix of nodes, ampersand replacement = \&] {
{12} \& {7} \& {2} \& {7} \& {2} \& {8}\\
};
\end{scope}
\path[draw] (A5-1-3.north west) -- (A5-1-4.north east) -- (B5-1-4.south east) -- (B5-1-4.south west) -- (A5-1-3.north west);
\end{tikzpicture}
\end{document}


Here \path[draw] groups 7s of the two matrices together. Is there any way to group them with a more "curvy" curve? i.e. by some curve that doesn't look so regular.

-

Like this (note that I replaced your last coordinate by -- cycle)?

\draw [rounded corners=5pt]
(A5-1-3.north west) -- (A5-1-4.north east) --
(B5-1-4.south east) -- (B5-1-4.south west) -- cycle;


or more like this?

\draw
[decoration={random steps,segment length=6pt,amplitude=1.5pt},
decorate, rounded corners=2pt]
(A5-1-3.north west) -- (A5-1-4.north east) --
(B5-1-4.south east) -- (B5-1-4.south west) -- cycle


I’d prefer the first one because it looks better matching to the style of printed text. The latter seems like some one attacked your paper ;-)

PS: I don’t know why the zig zag curve doesn’t close itself maybe one can fix this, please?

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Instead of cycle you can just repeat the first point to close the shape. –  percusse Jan 10 '12 at 2:15
@percusse: Yeah I know but that doesn’t give a rounded corner at this point too. –  Tobi Jan 10 '12 at 19:20

Replace the last line with:

\draw plot [smooth cycle,tension=0.3] coordinates {(A5-1-3.north west)  (A5-1-4.north east)  (B5-1-4.south east) (B5-1-4.south west)};


The option smooth cycle results in the points to be closed using a smooth curve (so you don't include the initial point twice as was the case in your original code).

The tension can be adjusted to suit. Also refer to Easy curves in TikZ.

\documentclass{standalone}
\usepackage{comment}

\usepackage{tikz,pgf}

\usetikzlibrary{fit,scopes,calc,matrix,positioning,decorations.pathmorphing}

\begin{document}

\begin{tikzpicture}
\begin{scope}
\matrix (A5) [matrix of nodes, ampersand replacement = \&] {
{7}  \& {2} \& {7} \& {7} \& {2} \& {8}\\
};
\end{scope}
\begin{scope}
\matrix (B5) at ([yshift=-2.5cm]A5-1-1.south) [anchor=B5-1-1.north, matrix of nodes, ampersand replacement = \&] {
{12} \& {7} \& {2} \& {7} \& {2} \& {8}\\
};
\end{scope}
\draw plot [smooth cycle,tension=0.3] coordinates {(A5-1-3.north west)  (A5-1-4.north east)  (B5-1-4.south east) (B5-1-4.south west)};
\end{tikzpicture}
\end{document}

-
This doesn't look too good for the start/end point, is there any way to fix that? –  Torbjørn T. Jan 9 '12 at 22:06
@TorbjørnT.: Have adjusted the code to fix this. Basically use smooth cycle and only list each point once. –  Peter Grill Jan 9 '12 at 22:17
Great, smooth cycle had escaped my attention. –  Torbjørn T. Jan 9 '12 at 22:38