arraysspacing
Sorry for my bad English.
How can I removing space between bracket and array environment and obtained results as used cases environment.
Thank you very much!
I use code
\[\left\{\begin{array}{l} x + y = 1\\ x - y = 2 \end{array}\right.\]
\[\begin{cases} x+y=1 \\ x-y=2\end{cases}.\]
The array (and tabular) environment sets struts in rows. The size of the struts can be reduced by using smaller values than 1 or \arraystretch:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\left\{
\renewcommand*{\arraystretch}{.5}
\begin{array}{lll}
C(\tau_{k,i})=0.5Q_e\ddot{q}_t^T\ddot{q}_t + 0.5R_e \theta^T \theta
& \text{when} &
t\neq t_v\\
\\
C(\tau_{k,i})=0.5Q_e\ddot{q}_t^T\ddot{q}_t + 0.5R_e \theta^T \theta +
P_{\text{viapoint}} & \text{when} & t=t_v\\
\\
\quad\quad P_{\text{viapoint}}
=10^{10}(q_{t}-q_{\text{viapoint}})^T(q_{t}-q_{\text{viapoint}})
\end{array}\right.
\end{equation}
\end{document}
You can also take a look at AmSLaTeX (package amsmath) that provides many environments for aligned/non-aligned equations and cases structures.
You want to avoid the \tabcolsep altogether; note also the correction for the null delimiter. You can use an optional argument to enlarge the leading in special cases.
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}
\usepackage{amsmath}
\newenvironment{system}[1][1.1]
{\renewcommand{\arraystretch}{#1}
\left\{\begin{array}{@{}l@{}}}
{\end{array}\right.\kern-\nulldelimiterspace}
\begin{document}
A centered formula for showing the center:
\[
\int_{-\infty}^{\infty}e^{-x^2}\,dx=\sqrt{\pi}
\]
The new \texttt{system} environment:
\[
\begin{system}
x^{n}+y^{n}=z^{n}\\
x^{m}+y^{m}=z^{m}
\end{system}
\]
Predefined \texttt{array} environment:
\[
\left\{%
\begin{array}{l}
x^{n}+y^{n}=z^{n}\\
x^{m}+y^{m}=z^{m}
\end{array}%
\right.
\]
A \texttt{system} environment with the optional argument:
\[
\begin{system}[1.5]
x^{n}+y^{n}=z^{n}\\
x^{m}+y^{m}=z^{m}
\end{system}
\]
\end{document}
Best Answer
Two options:
One with dedicated
alignedenvironment. And, other by playing with the dedicated\mkern<space>. An example is as follows:which would give you: