# Cayley's Matrix Notation

Cayley used the following notation in his original paper A Memoir on the Theory of Matrices 1 My attempt to reproduce the notation is shown below:

\documentclass{article}
\usepackage{amsmath,amssymb,graphicx}
\begin{document}
\scalebox{2.5}{\parbox{0.3\textwidth}{$$\renewcommand\arraystretch{0}\setlength\arraycolsep{0pt} (\mathrm{X}, \mathrm{Y}, \mathrm{Z}){=}\lower10pt\hbox{\begin{array}{r@{}c@{,\mkern10mu}c @{,\mkern10mu}c@{,\mkern10mu}c l} ( &a &b & c & )\\ \lvert& a' &b' & c' &\rvert\\ \lvert& a'' & b'' & c'' & \rvert\\ \end{array}}\mkern-6mu(x,y,z),$$}}
\end{document}


As you will observe the delimiters need to be improved. Any suggestions?

• is it just my eyes or am I right in thinking that on its own the () are symmetric pair but the overlapping )( symbol is using thinner more rounded )( to get more of an overlap so not using the matching parens for the outer borders of the matrices.... – David Carlisle Apr 25 '19 at 22:30
• more $(1,2,3\between 4,5,6)$ than $(1,2,3)\!( 4,5,6)$ – David Carlisle Apr 25 '19 at 22:34
• @DavidCarlisle No it is the same thickness. There is a link to the Royal Society paper jstor.org/stable/pdf/108649.pdf – Yiannis Lazarides Apr 25 '19 at 22:45
• Yes that is the link I used, I see egreg also used \between see this image copied from that pdf, the overlapping brackets are not the same shape as the non-overlapping ones – David Carlisle Apr 26 '19 at 7:05
• @YiannisLazarides I love old manuscripts. I didn't know the Cayley's matrix notation and I'll keep your question among my favorites. – Sebastiano Apr 26 '19 at 21:59

My proposal:

\documentclass{article}
\usepackage{amsmath,amssymb,graphicx}

\DeclareMathSymbol{A}{\mathalpha}{operators}{A}
\DeclareMathSymbol{B}{\mathalpha}{operators}{B}
\DeclareMathSymbol{C}{\mathalpha}{operators}{C}
\DeclareMathSymbol{D}{\mathalpha}{operators}{D}
\DeclareMathSymbol{E}{\mathalpha}{operators}{E}
\DeclareMathSymbol{F}{\mathalpha}{operators}{F}
\DeclareMathSymbol{G}{\mathalpha}{operators}{G}
\DeclareMathSymbol{H}{\mathalpha}{operators}{H}
\DeclareMathSymbol{I}{\mathalpha}{operators}{I}
\DeclareMathSymbol{J}{\mathalpha}{operators}{J}
\DeclareMathSymbol{K}{\mathalpha}{operators}{K}
\DeclareMathSymbol{L}{\mathalpha}{operators}{L}
\DeclareMathSymbol{M}{\mathalpha}{operators}{M}
\DeclareMathSymbol{N}{\mathalpha}{operators}{N}
\DeclareMathSymbol{O}{\mathalpha}{operators}{O}
\DeclareMathSymbol{P}{\mathalpha}{operators}{P}
\DeclareMathSymbol{Q}{\mathalpha}{operators}{Q}
\DeclareMathSymbol{R}{\mathalpha}{operators}{R}
\DeclareMathSymbol{S}{\mathalpha}{operators}{S}
\DeclareMathSymbol{T}{\mathalpha}{operators}{T}
\DeclareMathSymbol{U}{\mathalpha}{operators}{U}
\DeclareMathSymbol{V}{\mathalpha}{operators}{V}
\DeclareMathSymbol{W}{\mathalpha}{operators}{W}
\DeclareMathSymbol{X}{\mathalpha}{operators}{X}
\DeclareMathSymbol{Y}{\mathalpha}{operators}{Y}
\DeclareMathSymbol{Z}{\mathalpha}{operators}{Z}

\newsavebox{\cayleybox}
\newlength{\cayleyheight}
\newenvironment{cayleymatrix}
{\begin{lrbox}{\cayleybox}
$\begin{array}{@{\enspace}l*{\numexpr#1-1}{@{{,}\enspace}l}@{\enspace}}} {\end{array}$\end{lrbox}%
\setlength{\cayleyheight}{\dimexpr\ht\cayleybox+\dp\cayleybox}%
\kern-0.8pt
\vtop to \cayleyheight{\hbox{\vphantom{$\between$}}\leaders\vrule\vfill}%
\raisebox{\dimexpr\ht\strutbox-\ht\cayleybox}{\usebox\cayleybox}%
\vtop to \cayleyheight{\hbox{\vphantom{$\between$}}\leaders\vrule\vfill}%
\kern-0.8pt
}
\newcommand{\by}{\kern-0.4pt{\between}\kern-0.4pt}

\thinmuskip=6mu
\medmuskip=0mu
\thickmuskip=0mu

\begin{document}

$% page 17 (X,Y,Z)= (\begin{cayleymatrix}{3} a & b & c \\ a' & b' & c' \\ a'' & b'' & c'' \end{cayleymatrix} \by x,y,z)$

$% page 32 (\begin{cayleymatrix}{2} a & c \\ b & d \end{cayleymatrix} \by \begin{cayleymatrix}{2} a & b \\ c & d \end{cayleymatrix} \by \begin{cayleymatrix}{2} a & c \\ b & d \end{cayleymatrix} \by \begin{cayleymatrix}{2} a & b \\ c & d \end{cayleymatrix} ) = \bigl( (\begin{cayleymatrix}{2} a & c \\ b & d \end{cayleymatrix}\by \begin{cayleymatrix}{2} a & b \\ c & d \end{cayleymatrix}) \bigr)^2$

\end{document} • I love your pictures :-) Congratulations on all the answers. The question is among my favorites. – Sebastiano Apr 26 '19 at 22:00

Extending Bernard's idea slightly: ...but not quite up to the standards of egreg's nice solution:)

\documentclass{article}
\usepackage{array}
\newcounter{cayley}
\newcolumntype{L}{>{\stepcounter{cayley}%
\ifnum\value{cayley}=1\raisebox{-0.4ex}{(}\kern0.5ex\else\vline\fi}c@{}}
\newcolumntype{R}{@{}c<{\space\ifnum\value{cayley}=1\kern0.5ex\raisebox{-0.4ex}{)}\else\vline\fi}}
\newenvironment{cayley}{\setcounter{cayley}{0}\array{L*{#1}{c}R}}{\endarray}

\begin{document}

$\begin{cayley} &a & b & c &\\ &a' & b' & c' &\\ &a''& b''& c''&\\ \end{cayley} \qquad \begin{cayley} &a & b & c & d &\\ &a' & b' & c' & d' &\\ &a''& b''& c''& d''&\\ \end{cayley}$

\end{document}


A TikZ proposal. Similarly to Andrew's nice answer you can focus on typing the matrix.

\documentclass{article}
\usepackage{tikz}
\makeatletter% https://tex.stackexchange.com/a/85531/121799
\long\def\ifnodedefined#1#2#3{%
\@ifundefined{pgf@sh@ns@#1}{#3}{#2}%
}
\makeatother
\newcounter{CM}
\usetikzlibrary{matrix}
\newcommand{\CayleyMatrix}[]{\stepcounter{CM}%
\begin{tikzpicture}[baseline=(mat-\number\value{CM}-1-1.base),inner sep=2pt,#1]
\matrix[matrix of math nodes,ampersand replacement=\&] (mat-\number\value{CM})
{ #2
};
\ifnodedefined{mat-\number\value{CM}-2-1}{%
\draw[semithick] (mat-\number\value{CM}.south west) -- (mat-\number\value{CM}.south west|-mat-\number\value{CM}-1-1.south) to[out=135,in=-135]
(mat-\number\value{CM}.south west|-mat-\number\value{CM}-1-1.north)
(mat-\number\value{CM}.south east) -- (mat-\number\value{CM}.south east|-mat-\number\value{CM}-1-1.south) to[out=45,in=-45]
(mat-\number\value{CM}.south east|-mat-\number\value{CM}-1-1.north) ;}{
\draw[semithick] (mat-\number\value{CM}.south west|-mat-\number\value{CM}-1-1.south) to[out=135,in=-135]
(mat-\number\value{CM}.south west|-mat-\number\value{CM}-1-1.north)
(mat-\number\value{CM}.south east|-mat-\number\value{CM}-1-1.south) to[out=45,in=-45]
(mat-\number\value{CM}.south east|-mat-\number\value{CM}-1-1.north) ;
}
\end{tikzpicture}}
\begin{document}
$\CayleyMatrix{ X \&Y \& Z \\ }=\CayleyMatrix{ a \&b \& c \\ a' \&b' \& c' \\ a'' \& b'' \& c'' \\ }\!\!\CayleyMatrix{ x \&y \& z \\ }$
\end{document} Here is an approximation, with basic commands:

\documentclass{article}
\usepackage{amsmath,amssymb,graphicx}

\begin{document}

$\begin{array}{c@{}ccc@{}c} (\mkern 4.2mu{} & a &b & c &\mkern 4.2mu)\\[-0.31ex] \vline & a' &b' & c' & \vline \\ \vline & a'' &b'' & c''& \vline \end{array}$%

\end{document} 