Math & Science ⇒ Splitting formulae inside aligned equation

[pzinn]

This may be a standard question, but in 15 years of (la)TeX I still haven't found a proper solution to the following problem:
suppose I'm writing a long calculation of the form
X= X1
= X2
= X3
etc
I use amslatex align environment to get all the = signs aligned.
so far, so good.
now, what if one of the r.h.s., say X2, is too long to fit on a line?
I'd like to be able to split it in such a way that the first half is aligned due to the equal sign, and the second half is *shoved to the right*. but despite the plethora of (semi-useless) commands in amslatex, there seems to be no way to position that second half properly. I end up using something like
&=X2a \\ &\hskip{5cm} X2b \\
where the actual hskip has to be adjusted for each equation. This is a very unsatisfactory solution. Anyone know a better one?

[coachbennett1981]

"Shoved to the right" On the same line?

[pzinn]

no, shoved to the right on the next line (since it's too long to fit on one)

[Adrian10]

I have exactly the same problem...

[pzinn]

fine, I'll answer myself...
Here's a possibility, but clearly not optimal:

Code: Select all

\newcommand\rightalign[1]{\noalign{\vbox{\hfill $\displaystyle #1$}}}

\begin{align*}
A&=B1
\\
&=B2a
\\
\rightalign{B2b}
&=B3
\end{align*}

(in particular should probably do something about tags/eqnos)

[Stefan Kottwitz]

Great, thank you for posting the solution you found!

Stefan