# Spacing between elements in an array

I have the following table almost finished (I tried to make the code as much readable as I could)

\documentclass{article}
\usepackage[table]{xcolor}
\usepackage{tikz}
\usepackage{mathtools}
\usepackage{array}

\begin{document}
\begin{center}
\renewcommand{\arraystretch}{1.6}
\begin{equation*}
\begin{array}{ | >{\centering\arraybackslash$} p{4.0cm} <{$}
| >{\centering\arraybackslash$} p{4.0cm} <{$}
| >{\centering\arraybackslash$} p{4.0cm} <{$}
| } \hline
a+\infty=\infty & a-\infty=-\infty & \infty+\infty=\infty \\ \hline                              % End of 1st row

-\infty-\infty=-\infty & \infty\cdot\infty=\infty & -\infty\cdot\infty=-\infty \\ \hline         % End of 2nd row

\dfrac{a}{\infty}=0         &

\dfrac{a}{0}=
\left\{ \renewcommand{\arraystretch}{1}
\begin{tabular}{c}
$\infty$ si $a>0$\\
$-\infty$ si $a<0$
\end{tabular} \right.\ &

\infty^a=
\left\{ \renewcommand{\arraystretch}{1}
\begin{tabular}{c}
$\infty$ si $a>0$\\
$0$  si $a<0$
\end{tabular}\right.\ \\ \hline                                                                  % End of 3rd row

\infty^\infty=\infty&\infty^{-\infty}=0&

a^\infty=
\left\{ \renewcommand{\arraystretch}{1}
\begin{tabular}{c}
$\infty$ si $a>1$\\
$0$  si $0\leq a<1$
\end{tabular}\right.\ \\ \hline                                                                  % End of 4th row

\cellcolor{gray!25}& 0^a=0\text{ si $a>0$} &\cellcolor{gray!25}  \\ \hline                       % End of 5th row

\end{array}
\end{equation*}
\end{center}
\end{document}


Several problems here:

• I managed to make the columns to have the same width but I have to copy-paste that code every time I want to make a column with that property (maybe some redefinition with \renewcommand?)
• When I use tabular inside the array environment the curly brackets are too close from the cell limits, and I wonder if you can redefine the size of all the cells of those rows to fit those tables.
• Is there an option that array (or tabular) could get that stretch the array without having to use \renewcommand{\arraystretch}{<number>} every time I make a new table?

I'm looking for a general solution, not only for this problem, since I will define a lot of tables in my next report, and for sure a lot of people will appreciate a general solution since I see lots of questions about this mysterious world of LaTeX tables.

• One quick comment: \begin{center}\begin{equation*} is not a correct way to center equations. – user121799 Jan 31 '19 at 4:39

You can create a new column type this way:

\newcolumntype{C}{>{\centering\arraybackslash $}p{\mylen}<{$}}


and then use it in your array column definition:

\begin{array}{|C|C|C|}


\mylen is defined such as to have 3 columns with the same width but to not generate Overfull hbox (for the explanation, see, for example, here. I also used a smaller font size.

To enlarge the cell height I have used \mystrut{<length>} to put a gap before the content and \\[<length>] to put a gap after it. I didn't renew \arraystrech because this affects also the spacing in cases environment, which I used instead of tabular.

As marmot said in his comment, no need to put an equation environment in a center one, it is already centered.

\documentclass{article}
\usepackage[table]{xcolor}
\usepackage{mathtools}
\usepackage{array}
\usepackage{calc}
\newlength{\mylen}
\setlength{\mylen}{\linewidth/3-2\tabcolsep-\arrayrulewidth-\arrayrulewidth/3}
\newcolumntype{C}{>{\centering\arraybackslash $}p{\mylen}<{$}}
\newcommand{\mystrut}{\rule{0pt}{#1}}

\begin{document}
\begin{equation*}\small
\begin{array}{|C|C|C|}
\hline
\mystrut{12pt} a+\infty=\infty & a-\infty=-\infty & \infty+\infty=\infty \\[4pt]
\hline                              % End of 1st row
\mystrut{12pt} -\infty-\infty=-\infty & \infty\cdot\infty=\infty & -\infty\cdot\infty=-\infty \\[4pt] \hline         % End of 2nd row
\mystrut{26pt}\dfrac{a}{\infty}=0         &
\dfrac{a}{0}=
\begin{cases}
\infty  & \text{si }  a>0 \\
-\infty  & \text{si }  a<0
\end{cases} &
\infty^a=
\begin{cases}
\infty & \text{si }  a>0 \\
0  & \text{si }  a<0
\end{cases} \\[20pt]
\hline                                % End of 3rd row
\mystrut{26pt}\infty^\infty=\infty&\infty^{-\infty}=0&

a^\infty=
\begin{cases}
\infty & \text{si } a>1 \\
0  & \text{si } 0\leq a<1
\end{cases} \\[20pt]
\hline                                % End of 4th row
\cellcolor{gray!25}& \mystrut{14pt}0^a=0\text{ si $a>0$} &\cellcolor{gray!25}  \\[4pt]
\hline                       % End of 5th row
\end{array}
\end{equation*}

\end{document} • I decline any responsibility for the correctness of the math in this answer. – CarLaTeX Jan 31 '19 at 7:07
• I have laughed with that comment :) – Martín Jan 31 '19 at 11:42
• @Martín lol, thank you for accepting my answer :) – CarLaTeX Jan 31 '19 at 14:07