I am trying to align a multiline equation using array within the equation but it turns out it doesn't do very well. The code I am using is as follows:
\begin{equation} \begin{array}{lcl}
\mathcal{L}^{-1}\left\{f(d)\right\} &= \mathcal{L}^{-1}\left\{f_1(\delta).f_2(\delta)\right\} \\
& = exp(mt) \star \left\{\frac{l}{2\sqrt{\pi t^3}} exp(-l^2/{4t})\right\} \\
& = F_1 * F_2
\end{array}
\end{equation}
Can anyone suggest better way to deal with it ?
array is not designed for aligning equations, it is designed for arrays and matrices. The amsmath package has a host of alignment environments, I give a couple of examples:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
\mathcal{L}^{-1}\left\{f(d)\right\} &= \mathcal{L}^{-1}\left\{f_1(\delta).f_2(\delta)\right\} \\
& = \exp(mt) \star \left\{\frac{l}{2\sqrt{\pi t^3}} \exp(-l^2/{4t})\right\} \\
& = F_1 * F_2
\end{align}
or
\begin{equation}
\begin{aligned}
\mathcal{L}^{-1}\left\{f(d)\right\} &= \mathcal{L}^{-1}\left\{f_1(\delta).f_2(\delta)\right\} \\
& = \exp(mt) \star \left\{\frac{l}{2\sqrt{\pi t^3}} exp(-l^2/{4t})\right\} \\
& = F_1 * F_2
\end{aligned}
\end{equation}
\end{document}
note that exp is a multi-letter identifier so shouldn't be set in math italic.
David's solution is the correct way to go for this case, but you can use array for this and sometimes it does come in handy:
So, the changes required are:
left aligned, not right aligned.@{}, and use &{}= to get the proper math spacing around the equal signs.\exp instead of exp as that is an operator and not a variable.\cdot instead of . (unless the lower dot notation is something I am not familiar with).As David Carlisle commented, this formulas are displayed in the cramped \textstyle. If you desire the \displaystyle you need to add \displaystyle where it is needed (in this case the second line) to obtain:
Or, if you include the array pacakge then you can include the >{\displaystyle} style to the column specification (as illustrated in last part of MWE).
\documentclass{article}
\usepackage{amsmath}
\usepackage{array}
\begin{document}\noindent
Without \verb|\displaystyle|:
\begin{equation}
\begin{array}{l@{}l}
\mathcal{L}^{-1}\left{f(d)\right}
&{}= \mathcal{L}^{-1}\left{f_1(\delta) \cdot f_2(\delta)\right} \
&{}= \exp(mt) \star \left{\frac{l}{2\sqrt{\pi t^3}} \exp(-l^2/{4t})\right} \
&{}= F_1 * F_2
\end{array}
\end{equation}
With \verb|\displaystyle|:
\begin{equation}
\begin{array}{l@{}l}
\mathcal{L}^{-1}\left{f(d)\right}
&{}= \mathcal{L}^{-1}\left{f_1(\delta) \cdot f_2(\delta)\right} \
&{}= \displaystyle\exp(mt) \star \left{\frac{l}{2\sqrt{\pi t^3}} \exp(-l^2/{4t})\right} \
&{}= F_1 * F_2
\end{array}
\end{equation}
With \verb|\displaystyle| and \verb|array| package:
\begin{equation}
\begin{array}{l@{}>{\displaystyle}l}
\mathcal{L}^{-1}\left{f(d)\right}
&{}= \mathcal{L}^{-1}\left{f_1(\delta) \cdot f_2(\delta)\right} \
&{}= \exp(mt) \star \left{\frac{l}{2\sqrt{\pi t^3}} \exp(-l^2/{4t})\right} \
&{}= F_1 * F_2
\end{array}
\end{equation}
\end{document}
You can eliminate the need for using &{}= by burying that in the array column spec:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\begin{array}{l@{{}={}}l}
\mathcal{L}^{-1}\left{f(d)\right}
& \mathcal{L}^{-1}\left{f_1(\delta).f_2(\delta)\right} \
& \exp(mt) \star \left{\frac{l}{2\sqrt{\pi t^3}} \exp(-l^2/{4t})\right} \
& F_1 * F_2
\end{array}
\end{equation}
\end{document}
\textstyle not \displaystyle
– David Carlisle
Mar 27 '13 at 23:13
I always need to line up equals signs outside of a math environment, the best thing I found was to use center and tabular. This was best for lining up my equals signs in proofs, and in variable descriptions.
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\int_{a}^{b} f(x) dx \approx h \left[ \dfrac{f(a)}{2} + \sum_{i=1}^{\eta} f(x_i) +
\dfrac{f(b)}{2}\right]
\end{equation}
where
\begin{center}\begin{tabular}{ccl}\
$a, b$ & = & bounds of integration (endpoints of interval) \\
$f(x)$ & = & function \\
$h$ & = & step size \\
$\eta$ & = & number of trapezoids
\end{tabular}\end{center}
\begin{align}then it would put three equations on three lines. I just want only one. – Jdbaba Mar 27 '13 at 23:02\notag) sometimes things are clearly one long equation that you need to wrap, for chained=you can think of it as lots of equations or one long one, anyway it's your document you can get to choose (there are other choices such as gathered and split as well...) – David Carlisle Mar 27 '13 at 23:08aligned. Is there any reason ?\begin{equation} \begin{aligned} F_1 \star F_2 = \int_0^t e^{m(t-\tau)} \frac{l}{2\sqrt{\pi t^3}} e^{\frac{-l^2}{4t}} \& = \frac{l e^{mt}}{2\pi^{1/2}}\int_0^t \frac{e^{(-(m\tau+l^2/{4t}))}}{\tau ^{3/2}} \end{aligned} \end{equation}– Jdbaba Mar 27 '13 at 23:12&before the first=? – David Carlisle Mar 27 '13 at 23:14