Re: New math feature requests

[Aditya Mahajan <adityam@umich.edu>]

On Tue, 8 Aug 2006, Aditya Mahajan wrote:
> 3. Formula tagging
>
> amsmath allows formulas to be tagged. I will explain amsmath's
> behaviour and hope that Hans can come up with the context way of doing
> such things.
>
> Occasionally, one wants to tag a formula, e.g.
>
> \placefomrula[a] \startformula
>   a x = b
> \stopformula
>
> \placetaggedformula[b]{*} \startformula
>   x = \frac {b}{a}
> \stopformula
>
> should come out as
>
>         a x = b              (1)
>         x = b/a              (*)
>
> Notice that ( and ) correspond to left and right in setupformulas. It
> should also be possible to place a tag without these brackets, so
>
> \placetaggedformulawithoutbrackets[c]{**} \startformula
>   b = ax
> \stopformula
>
> should come out as
>        b = ax               ** <--- no brackets here
>
> Maybe, instead of placetaggedformulawithout brackets, one can simply
> have
>
> \placetaggedformula[c][left=,right=]{**}
>
> but in such cases it is easy to get confused with the reference and
> options. I am not sure what is a good way to do this.
>
> It should also be possible to refer to these tagged formulas. So
> \in{formula}[b] should give * and \in{formula}[c] should give **.
>
> The tag should be set in text mode, so that one can say
> \placetagformula {Answer} and the Answer will come out in text 
mode.

I got an idea of using conversion for formula tagging. For single line 
formulas, the idea is pretty simple. I define a dummyconversion which 
always maps to the tag and set the formula conversion to 
dummyconversion. Then, I save the formula number, let startformula, 
work as normal and refine stopformula to restore formula number. 
The internal macros take care of referencing.

This is my first attempt

%------------------------8<--------------------------
\def\placeformulatag%
   {\dosingleempty\doplaceformulatag}

\def\doplaceformulatag[#1]#2%
   {\let\normalstopformula\stopformula
    \def\stopformula%
     {\normalstopformula
      \restorenumber[formula]
      \egroup
      \let\stopformula\normalstopformula}
      \bgroup
      \savenumber[formula]
      \def\dummyconversion##1{#2}
      \defineconversion[dummyconversion][\dummyconversion]
      \setupformulas[conversion=dummyconversion]
      \placeformula[#1]}


\starttext
\placeformulatag[tag]{test} \startformula
   E = mc^2
\stopformula

See \in formula[tag] for a tagged formula
\stoptext
%----------------------------8<-------------------------

This one places (test) with the brackets in place of the formula 
number. It is easy to get rid of the brackets by using 
\setupformulas[left=,right=]. However, I do not know what will be a 
good interface for this.

In Latex, \tag{whatever} give (whatever) and \tag*{whatever} gives 
whatever without the brackets. But context does not use starred form 
of commands, and I do not want to introduce them here. One way is

\placeformulatag[ref][left=,right=] {my tag} ....

Is this fine? We can also have tagleft=... and tagright=... as part of 
setupformulas, or, if that is too confusion, have 
\setupformulatagging[left=...,right=...].

However, this idea does not work inside \startmathalignment as the 
conversion can not be changed inside a formula.

\placeformula \startformula \startalign
   \NC a \NC = b \NR[+]
   \setupformulas[conversion=set 1]
   \NC c \NC = d \NR[+]
\stopalign \stopformula

Is there some better way to achieve the same effect inside a 
mathalignment?

Aditya