Tweaking a Multiplication Table

[topsquark]

I recently posted a couple of multiplication tables and I feel it needs a tweak:

\(\displaystyle \begin{array}{c||c|c|c|c|}
V & e & a & b & c \\
\hline \hline
e & e & a & b & c \\
a & a & e & c & b \\
b & b & c & e & a \\
c & c & b & a & e
\end{array}
\)

The LaTeX on the forum doesn't like the double lines || or = (as lines, not the equal sign!). Does anyone know how to make the lines bold faced or something? I feel the top line and first vertical line should be singled out in some way.

-Dan

 

[I like Serena]

Hey Dan,

There are some suggestions in https://mathhelpboards.com/tikz-pictures-63/4-element-4-element-multiplication-table-21434.html.
In particular a MathJAX suggestion and a TikZ suggestion.

To summarize:

One way is to keep only those two lines and remove all the others: $$\begin{array}{c|cccc} + & a&b&c&d \\ \hline a&a&b&c&d\\ b&b&a&d&c \\ c&c&d&a&b \\ d&d&c&b&a \end{array}.$$

My previous TikZ suggestion had the 'problem' that math symbols had to have \$ symbols around them.
Turns out there is a better way by using a [M]matrix of math nodes[/M] instead of a [M]matrix of nodes[/M].
Then all nodes are already in math mode.
Other than that the solution is the same.
\begin{tikzpicture}
\usetikzlibrary{matrix}

\matrix (m) [nodes={minimum width=3em,minimum height=3ex},matrix of math nodes]
{
\times & 0 & 1 & \theta & \theta + 1 \\
0 & 0 & 0 & 0 & 0\\
1 & 0 & 1 & \theta & \theta + 1\\
\theta & 0 & \theta & \theta + 1 & 1 \\
\theta + 1 & 0 & \theta + 1 & 1 & \theta \\
};

\draw[very thick] (m-1-1.north east) -- (m-5-1.south east);
\draw[very thick] (m-1-1.south west) -- (m-1-5.south east);
\foreach \x in {2,...,5}{
\draw (m-1-\x.north east) -- (m-5-\x.south east);
\draw (m-\x-1.south west) -- (m-\x-5.south east);
}
\end{tikzpicture}
[latexs]\begin{tikzpicture}
\usetikzlibrary{matrix}

\matrix (m) [nodes={minimum width=3em,minimum height=3ex},matrix of math nodes]
{
\times & 0 & 1 & \theta & \theta + 1 \\
0 & 0 & 0 & 0 & 0\\
1 & 0 & 1 & \theta & \theta + 1\\
\theta & 0 & \theta & \theta + 1 & 1 \\
\theta + 1 & 0 & \theta + 1 & 1 & \theta \\
};

\draw[very thick] (m-1-1.north east) -- (m-5-1.south east);
\draw[very thick] (m-1-1.south west) -- (m-1-5.south east);
\foreach \x in {2,...,5}{
\draw (m-1-\x.north east) -- (m-5-\x.south east);
\draw (m-\x-1.south west) -- (m-\x-5.south east);
}
\end{tikzpicture}[/latexs]