# Diagonal line in math arrays

I have some arrays in math mode, such as the one below. I would like a diagonal line in a cell, something like diagbox (diagobx package) or diaghead (makecell package). But it seems that diagbox and diaghead only work in a tabular environment. Of course a way to go consists in using tabular instead of array but this requires to put some $'s in each cell. I'm looking for a less tedious solution. \documentclass{article} \usepackage{diagbox} \begin{document} $$\begin{array}{r|cccc} %\diagbox{x}{y} & (0,0) & (0,1) & (1,0) & (1,1) \\ \hline (0,0) & \phi^{-1} & \frac{f_n}{f_{n-1}} - \phi^{-1} & 0 & \frac{f_{n+1}}{f_{n-1}} \\ (0,1) & f_{n}/f_{n-1} & 0 & f_{n+1}/f_{n-1} & 0 \\ (1,0) & \phi^{-1} & \phi^{-2} & 0 & 0 \\ (1,1) & 1 & 0 & 0 & 0 \\ \end{array}$$ \end{document}  • Doesn't M. Al Jumaily's answer sufficient? – user108724 Apr 14, 2020 at 13:40 ## 2 Answers Just encapsulate \diagbox{x}{y} inside an \hbox{}, i.e., \hbox{\diagbox{x}{y}}. Also, you can surround the text with $...$ to ensure the text is in mathmode as such: \hbox{\diagbox{$x$}{$y$}}. Off-topic, you should be using $...$ instead of $$...$$ (have a look here). \documentclass{article} \usepackage{diagbox} \begin{document} \noindent\ Without \$...\$$\begin{array}{r|cccc} \hbox{\diagbox{x}{y}} & (0,0) & (0,1) & (1,0) & (1,1) \\ \hline (0,0) & \phi^{-1} & \frac{f_n}{f_{n-1}} - \phi^{-1} & 0 & \frac{f_{n+1}}{f_{n-1}} \\ (0,1) & f_{n}/f_{n-1} & 0 & f_{n+1}/f_{n-1} & 0 \\ (1,0) & \phi^{-1} & \phi^{-2} & 0 & 0 \\ (1,1) & 1 & 0 & 0 & 0 \\ \end{array}$ With \$...\$$\begin{array}{r|cccc} \hbox{\diagbox{x}{y}} & (0,0) & (0,1) & (1,0) & (1,1) \\ \hline (0,0) & \phi^{-1} & \frac{f_n}{f_{n-1}} - \phi^{-1} & 0 & \frac{f_{n+1}}{f_{n-1}} \\ (0,1) & f_{n}/f_{n-1} & 0 & f_{n+1}/f_{n-1} & 0 \\ (1,0) & \phi^{-1} & \phi^{-2} & 0 & 0 \\ (1,1) & 1 & 0 & 0 & 0 \\ \end{array}$ \end{document}  A better solution: since diagbox always use \tabcolsep and \arraycolsep may have a different value, we need to do this: \newcommand\mydiagbox[2]{\hbox{\tabcolsep=\arraycolsep\diagbox{$#1$}{$#2\$}}}

Then we can use \mydiagbox{X}{Y} inside array environment.