Re: \startalign and "underline"

[Aditya Mahajan <adityam@umich.edu>]

On Tue, 13 Feb 2007, Mojca Miklavec wrote:

> Hello,
>
> is there a nice way to [mis]use \startalign or combine it with
> something else to typeset equations like the following one (in a
> fixed-width font)?

fixed-width font? Then you can just use \starttable with appropriate 
setting for distance. Even otherwise you can use starttable with |m| 
columns, but I understant math align better.

>
>   a + b =  9
>   a - b =  3
>  ___________
>  2a     = 12

\noalign is your friend. Here is the first approximation

\starttext

\startformula \startalign[n=5]
   \NC a  \NC + \NC b \NC = \NC 9  \NR
   \NC a  \NC - \NC b \NC = \NC 3  \NR
\noalign{\hrule}
   \NC 2a \NC   \NC   \NC = \NC 12 \NR
\stopalign \stopformula

\stoptext

Hmm... the width of the rule is too long, so lets use something with a 
fixed width

\starttext

\startformula \startmatrix[n=5]
   \NC a  \NC + \NC b \NC = \NC 9  \NR
   \NC a  \NC - \NC b \NC = \NC 3  \NR
\noalign{\hrule}
   \NC 2a \NC   \NC   \NC = \NC 12 \NR
\stopmatrix \stopformula

\stoptext

Hmm... distance and alignment are wrong, so lets correct that

\starttext

\startformula

\startmatrix[n=5,distance=.3em,align={right,middle,right,middle,right}]
   \NC a  \NC + \NC b \NC = \NC 9  \NR
   \NC a  \NC - \NC b \NC = \NC 3  \NR
\noalign{\hrule}
   \NC 2a \NC   \NC   \NC = \NC 12 \NR
\stopmatrix \stopformula

\stoptext

Voila! I did not know that ConTeXt math alignment macros could do 
something like this.

Aditya