# right bind when using align

I have multiple lines of equations in align environment, some of those are to long and I have to split them. How can I make the second line rightbound? What I do now is:

\documentclass[oneside,a4paper]{hepthesis}
\usepackage{amssymb}

\begin{document}
\begin{align}
a &= blabla
a &= loooooooooooooooooooooooooooongexpression \notag \\
& + \text{~~~~~~~~~~~} loooooooooooooooooooooooooooongexpression
\end{align}
\end{document}


Which is of course quite ugly and in now way as it supposed to be done.

-
A dirty trick is to use \hspace{1000pt} and then check the size of the resulting overfull hbox in the log file. If it's overfull by n points, change 1000 to 1000 - n. –  Ian Thompson Apr 11 '14 at 9:59
Probably the multlined environment of mathtools can help. –  egreg Apr 11 '14 at 9:59

There is no concept of “right bound”. You can use two strategies that differ for how the equation number is placed.

## multlined (from the mathtools package)

\documentclass[oneside,a4paper]{hepthesis}
\usepackage{mathtools,amssymb}

\begin{document}

\begin{align}
a &= blabla \\
a &= \begin{multlined}[t]
loooooooooooooooooooooooooooongexpression \\
loooooooooooooooooooooooooooongexpression
\end{multlined}
\end{align}

\end{document}


## split inside align

Note the tbtags option for amsmath. Without it, the number would be placed vertically centered with respect to the split.

\documentclass[oneside,a4paper,tbtags]{hepthesis}
\usepackage{amssymb}

\begin{document}

\begin{align}
a &= blabla \\
\begin{split}
a &= loooooooooooooooooooooooooooongexpression \\
\end{split}
\end{align}

\end{document}


-
In my view, the indentation should depend on the expression, if the break is at a non-fenced binary (like a +), then I don't think there should be any extra indentation (other than getting the + aligned on the right of the =. –  daleif Apr 11 '14 at 10:20
@daleif I agree, but it depends on the expressions which we don't know the content of. –  egreg Apr 11 '14 at 10:22
Multilined did the trick thank you. –  magu_ Apr 11 '14 at 11:19

If you want to "right bind" the last part ot an equation, you'll have to play with flalign and the \mathllap (and incidentally \mathrlap) command defined by the mathtools package:

\documentclass[11pt, oneside,a4paper]{report}
\usepackage{mathtools}
\usepackage[showframe, nomarginpar]{geometry}

\begin{document}

\begin{flalign}
&  &     a &= blabla  &  & \mbox{\,}\\
&  &    a &= loooooooooooooooooooooooooooongexpression   \notag \\[-4pt]
&  &     & &&\mathllap{+ ~~~~~~~~~~~loooooooooooooooooooooooooooongexpression}
\end{flalign}

\begin{flalign}
&  &     a &= blabla  &  & \mbox{\,}\\
&  &    a &= loooooooooooooooooooooooooooo\mathrlap{ngexpression}  &  & {\,}  \notag \\[-4pt]
&  &     & &&\mathllap{+ ~~~~~~~~~~~loooooooooooooooooooooooooooongexpression}
\end{flalign}

\end{document}


-