# How may I left-align the following array?

I would not like it to be centred.

\documentclass[11pt,a4paper]{article}
\usepackage{blindtext}
\usepackage{mathtools}

\begin{document}
$a^{'}_{ij}=\left\{\begin{array}{lr} a_{ij}&\: \text{(i\neq r;\: i\neq s)}\\ a_{sj}&\: \text{(i=r)}\\ a_{rj}&\: \text{(i=s)} \end{array}\right.$\\
\end{document}

-

You should use cases:

\documentclass[11pt,a4paper]{article}
\usepackage{mathtools}

\begin{document}
$a^{'}_{ij}=\begin{cases} a_{ij}& (i\neq r;\quad i\neq s)\\ a_{sj}& (i=r)\\ a_{rj}& (i=s) \end{cases}$
\end{document}


Or do you mean this?

\documentclass[11pt,a4paper]{article}
\usepackage{mathtools,showframe}  %% Remove showframe

\begin{document}
\noindent
$\displaystyle a^{'}_{ij}=\begin{cases} a_{ij}& (i\neq r; \quad i\neq s)\\ a_{sj}& (i=r)\\ a_{rj}& (i=s) \end{cases}$
\end{document}


If it is latter, you may also use flalign*

\documentclass[11pt,a4paper]{article}
\usepackage{mathtools,showframe}  %% Remove showframe

\begin{document}
\noindent
\begin{flalign*}
&a^{'}_{ij}=\left\{\begin{array}{lr}
a_{ij}& (i\neq r; \quad i\neq s)\\
a_{sj}& (i=r)\\
a_{rj}& (i=s)
\end{array}\right.&
\end{flalign*}
\end{document}


-
Brilliant! You provide the precise answer I looked for. Thank you so very much, Harish! I think this is the second time, you have provided me an answer. Are you on Facebook? :) – Nisal Kevin Kotinkaduwa Sep 4 '14 at 14:31
@Harish Kumar: What's the use of the \text commands since they contain only maths? – Bernard Sep 4 '14 at 15:48
@Bernard - It looks like it's a holdover from the OP's code that didn't get simplified/streamlined. I agree that the \text wrappers and the interior \$ directives should be omitted. – Mico Sep 4 '14 at 17:39
@Bernard No use. I was too sleepy!. Now cleaned. Thanks. – Harish Kumar Sep 4 '14 at 22:20
@NisalKevinKotinkaduwa Yes , I am. Search for harish kumar holla – Harish Kumar Sep 5 '14 at 0:52