Re: A few questions about aligned maths

[Aditya Mahajan <adityam@umich.edu>]

On Thu, 13 Mar 2008, Morgan Brassel wrote:
> 3) Aditya, I saw your remark in your 'My Way' concerning the 'multline'
> environment. I must admit I would really be glad to see it appear in
> ConTeXt! I'm afraid I'm not able to implement it myself... I use it a
> lot with amsmath: when a formula is just too long for one line, I put it
> on two with multline. The first part of the formula is left aligned on the
> first line, and the second part is right aligned on the second line. It seems
> impossible to get the same result with only 'align'. Would it be difficult
> to make it available in ConTeXt?

Here is my first attempt. Completely bare-bones right now, but short 
enough to show what needs to be done.

\unprotect
\def\startmathlines
   {\def\stop@math{$}
    \def\NC{}
    \def\NR{\def\NC{\cr}}
    % Hack for number. Should be done by measuring the width of the number
    \scratchdimen\dimexpr\displaywidth-4em \relax
    \vbox \bgroup
    \halign\bgroup
     \hbox to \scratchdimen
       {\hfil \strut
         $\mathsurround\zeropoint\displaystyle{}## \stop@math
        \hfil}%
        \crcr
        \hfilneg}

\def\stopmathlines
   {\hfilneg
    \crcr
    \egroup
    \egroup}
\protect

\starttext

\placeformula \startformula \startmathlines
   \NC f(x) = (a+b)^n \NR
   \NC = a^n + n \cdot a^{n-1} b + \cdots + n \cdot a b^{n-1} + b^n \NR
   \NC = a^n + n \cdot a^{n-1} b + \cdots + n \cdot a b^{n-1} + b^n \NR
\stopmathlines \stopformula

\stoptext

Taking care of [align=left|right] should be easy. This version will not 
break across pages. I cannot figure out how to get rid of the outer \vbox. 
Any suggestions?

Aditya
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