align中某式子加框

kuing

转自Some LATEX2ε tricks and tips (IV) Luca Merciadri

1. \makeatletter
2. \newcommand\Aboxed[1]{%
3. % syntax: \Aboxed{ left & right }
4. \@Aboxed#1\ENDDNE}
5. \def\@Aboxed#1&#2\ENDDNE{%
6. % idea: get the left and right part
7. % typeset them in a \boxed AFTER an ‘&’
8. % and pull it backwards
9. % but in order to get the horizontal
10. % placement to work we need to set
11. % some appropriate space to the left
12. % of the ‘&’
13. \settowidth\@tempdima{$\displaystyle#1{}$}%
14. \setlength\@tempdima
15. {\@tempdima+\fboxsep+\fboxrule}
16. % \global does not always mix well
17. % with \setlength
18. \global\@tempdima=\@tempdima
19. \kern\@tempdima
20. &
21. \kern-\@tempdima
22. \boxed{#1#2}%
23. }
24. \makeatother

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然后

1. \begin{align*}
2. \Aboxed{A&=B}\\
3. A&=B\\
4. &=C
5. \end{align*}

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