# How to get align or similar equation environment to use the whole line instead of centering around the equality sign

I'm creating a Beamer presentation in which a line in the equation environment should fill the whole screen and should not only be centered arround the equality sign. I think this looks nicer and is much more readable for the audience. Actually using \multline on just one line gives me exactly that. How can I have that behaviour with \align or any other 'equation aligning' environment? Here is a comparison, I want to achieve the above with an alignment like below:

\documentclass{beamer}
\usepackage{amsmath}
\usepackage[thicklines]{cancel}
\usepackage{color}
\definecolor{Blue}{rgb}{0,0,1}
\definecolor{Red}{rgb}{1,0,0}

\begin{document}
\begin{frame}
\begin{multline*}
\frac{\partial s_{\mu}}{\partial x_\mu}=
A \;[\ccancel{ \frac{\partial \phi^*}{\partial x_{\mu}}
\frac{\partial \phi}{\partial x_{\mu}}}{Red}
-\ccancel{\vphantom{\frac{1}{1}}(\square \phi^*)\phi}{Blue}
+\ccancel{\vphantom{\frac{1}{1}(kk)}\phi^* \square\phi}{Blue}
-\ccancel{\frac{\partial \phi^*}{\partial x_{\mu}}
\frac{\partial \phi}{\partial x_{\mu}}}{Red}]
\end{multline*}
\\[2em]
\begin{align*}
\frac{\partial s_{\mu}}{\partial x_\mu} & = A \;[\ccancel{ \frac{\partial \phi^*}{\partial x_{\mu}}
\frac{\partial \phi}{\partial x_{\mu}}}{Red}
-\ccancel{\vphantom{\frac{1}{1}}(\square \phi^*)\phi}{Blue}
+\ccancel{\vphantom{\frac{1}{1}(kk)}\phi^* \square\phi}{Blue}
-\ccancel{\frac{\partial \phi^*}{\partial x_{\mu}}
\frac{\partial \phi}{\partial x_{\mu}}}{Red}] \\
& = 0
\end{align*}

\end{frame}
\end{document}


-
the first equation has an extremely lousy typesetting which you shouldn't use. – Herbert Jan 13 '13 at 19:02
I don't think it's lousy if you consider it for a beamer presentation. As stated above my opinion is that it's more readable in that case. For a common article I would agree with you, but not for a presentation! – user24357 Jan 13 '13 at 19:16
This might be a matter of personal taste but I find the second one far more readable than the first which IMHO more looks like single fragments than like a whole equation... – clemens Jan 13 '13 at 19:23

I don't like very much cancellation signs. However here's a proposal; notice that I defined two new commands: one for simplifying the input, the second one to get the right spacing for the Laplacian.

\documentclass{beamer}
\usepackage{amsmath}
\usepackage[thicklines]{cancel}
\usepackage{color}
\definecolor{Blue}{rgb}{0,0,1}
\definecolor{Red}{rgb}{1,0,0}
\newcommand{\pder}[2]{\frac{\partial#1}{\partial#2}}
\DeclareMathOperator{\lapl}{\square}

\begin{document}
\begin{frame}
\begin{align*}
\pder{s_{\mu}}{x_\mu} &=
A\biggl[
\ccancel{\pder{\phi^*}{x_{\mu}}\pder{\phi}{x_{\mu}}}{Red}
-\ccancel{\vphantom{\dfrac{1}{1}}\bigl(\lapl\phi^*\bigr)\phi}{Blue}
+\!\ccancel{\hphantom{\big(}\vphantom{\dfrac{1}{1}}\phi^*\lapl\phi\hphantom{\big)}}{Blue}\!
-\ccancel{\pder{\phi^*}{x_{\mu}}\pder{\phi}{x_{\mu}}}{Red}
\biggr]
\\[3ex]
&=0
\end{align*}

\end{frame}
\end{document}


I made also some adjustments for getting the same inclination of the blue bars.

-
and to fill more of the width it is possible to enclose the align* in a group with \Large. But then, there isn't that much room left for additional material on the frame... but if it is a presentation, I hope the room has an old-fashioned blackboard so that the true explanations can be given with the chalk... – jfbu Jan 14 '13 at 20:05
This is the way I've done it now, with a \Large in front. Thank you everybody contributing to this question! – user24357 Jan 27 '13 at 10:19

I have to agree with Herbert for two reasons i) The location of terms might indeed be more readable but also more ambigous, ii) small brackets look like a condition that renders the partial expression is equal to A and you are reminding it similar to a(t)=b(t) [almost everywhere]

I would suggest the following where the cancellation is slightly more obvious and color free.

\documentclass{beamer}
\usepackage{mathtools,lmodern,xcolor}

\definecolor{Blue}{rgb}{0,0,1}
\definecolor{Red}{rgb}{1,0,0}

\begin{document}
\begin{frame}

\begin{align*}
\frac{\partial s_{\mu}}{\partial x_\mu} & = A \left(
\underbracket[0.5pt][3pt]{\frac{\partial \phi^*}{\partial x_{\mu}}\frac{\partial \phi}{\partial x_{\mu}}
-\underbracket[0.5pt][3pt]{\vphantom{\frac{\partial}{\partial_\mu}}\square \phi^*\phi+\phi^* \square\phi}_{0}{}
-\frac{\partial \phi^*}{\partial x_{\mu}}\frac{\partial \phi}{\partial x_{\mu}}}_{0}\right) \\[2em]
& = 0
\end{align*}

\end{frame}
\end{document}


-
And may be \Biggl( and \Biggr) instead of those looong parenthesis? I like this answer, but personally, I don't like \left and \right here. By the way, you need to add {} after the first undergracket in order to get correct spacing between the minus and the last object. – Manuel Jan 13 '13 at 19:45
@Manuel I actually made it on purpose to draw the attention to the cancellations. Otherwise it looks like drawn later on top of the expression (or at least that's how I feel) but you are right on the minus sign. – percusse Jan 13 '13 at 21:45