[texhax] fbox in align environment

[Sebastian Canagaratna]

Phil: 

  I am having some problem getting your code to work. i am using
texlive, the latest version. I am unfamiliar with the 3D format you are
using for lengths. I presume this stands for the space occupied by "3D"?
Whatever it is, here is the error message I get:

ERROR: Illegal unit of measure (pt inserted).

--- TeX said ---
<to be read again> 
                   D
l.13 \alignboxedsep=3D1
                       pt
--- HELP ---
If you just got a

      ! Missing number, treated as zero.

error, then this is part of the same problem.  If not, it means that
LaTeX was expecting a length as an argument and found a number
instead.  The most common cause of this error is writing 0 instead of
something like 0in for a length of zero, in which case typing return
should result in correct output. However, the error can also be caused
by omitting a command argument.

Just in case my mailer mangled the code, here is what I am using:

\documentclass{article}
\usepackage{amsmath}
\def\alignboxed#1&#2\endalignboxed{%
  \bgroup
  \fboxsep=3D\alignboxedsep
  \rlap{\boxed{#1#2}}\hphantom{#1\kern\fboxsep}
  \egroup
}
\newlength{\alignboxedsep}
\alignboxedsep=3D1pt
\begin{document}
\begin{align}
  f_1(x) &=3D a+bx,
\\
  \alignboxed
  f_2(x) &=3D a+bx+cx=B2,
  \endalignboxed
\\
  \alignboxed
  f_3(x) &=3D a+bx+cx=B2+dx=B3.
  \endalignboxed
\end{align}
\begin{align*}
  x+y+2    & =3D 1
\\
  2x+3y-4z & =3D 2
\\
  \alignboxed
  3x-2y+z  & =3D3
  \endalignboxed
\\
  \alignboxed
  a & =3D b+c+d
  \endalignboxed
\end{align*}
\end{document}
I will experiment to see whether I can solve it on my own. Since you
have tested it, I presume my mailer introduced some character. I'll try
and track it down. Thanks.

Sebastian

On Wed, Jun 17, 2009 at 04:13:59PM +0200, Philip G. Ratcliffe wrote:
> Here's a more self-contained version, which should handling alignmnet better
> and allows for changing of \fboxsep via \alignboxedsep:
> 
> \documentclass{article}
> \usepackage{amsmath}
> \def\alignboxed#1&#2\endalignboxed{%
>   \bgroup
>   \fboxsep=\alignboxedsep
>   \rlap{\boxed{#1#2}}\hphantom{#1\kern\fboxsep}
>   \egroup
> }
> \newlength{\alignboxedsep}
> \alignboxedsep=1pt
> \begin{document}
> \begin{align}
>   f_1(x) &= a+bx,
> \\
>   \alignboxed
>   f_2(x) &= a+bx+cx²,
>   \endalignboxed
> \\
>   \alignboxed
>   f_3(x) &= a+bx+cx²+dx³.
>   \endalignboxed
> \end{align}
> \begin{align*}
>   x+y+2    & = 1
> \\
>   2x+3y-4z & = 2
> \\
>   \alignboxed
>   3x-2y+z  & =3
>   \endalignboxed
> \\
>   \alignboxed
>   a & = b+c+d
>   \endalignboxed
> \end{align*}
> \end{document}
> 
> Cheers,  Phil
>