# Remove whitespace left of an array

I would like to display equations one on top of the other with a large brace on the left, with the array environment for instance. However, there always is a consequential white space between the brace and the equations :

Code for the above example :

\documentclass{standalone}
\usepackage{amsmath,amssymb}

\begin{document}
$$\left\lbrace \begin{array}{l} x^2 + y^2 = R \\ x>0 \end{array} \right.$$
\end{document}


Is there a way to remove said white space ?

• Simply use the cases environment instead. – Bernard Jun 13 '20 at 15:08

The environment {array} adds a length equal of \arraycolsep on both sides of the array. In the documentation of amsmath, you read:

The extra space of \arraycolsep that array adds on each side is a waste so we remove it [in {matrix}] (perhaps we should instead remove it from array in general, but that’s a harder task).

In order to delete those spaces, you have to add @{} in the preamble in order to replace the \arraycolsep by nothing (the {} in @{}).

\documentclass{standalone}
\usepackage{amsmath,amssymb}

\begin{document}
$$\left\lbrace \begin{array}{@{}l@{}} x^2 + y^2 = R \\ x>0 \end{array} \right.$$
\end{document}


As suggested by @Bernard in the comments, you could use the cases environment from amsmath. Alternatively, you could reduce the spacing between the brace and the equations by placing @{} before the l column specified in the array.

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

\begin{document}
Original: $$\left\lbrace \begin{array}{l} x^2 + y^2 = R \\ x>0 \end{array} \right.$$

With \verb|cases|: $$\begin{cases} x^2 + y^2 = R \\ x>0 \end{cases}$$

Reducing space: $$\left\lbrace \begin{array}{@{}l} x^2 + y^2 = R \\ x>0 \end{array} \right.$$
\end{document}


In the third example, you could also adjust the spacing according to your needs, since the @{} will place what's between the brackets at that place in every row of the array. So a space can be added by replacing @{} with @{\,} or @{\;}, for instance.

• That's perfect, thanks – vic.col961 Jun 13 '20 at 15:25