Systems of equations in ConTeXt

Question

In LaTeX+amsmath, I can say

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{equation*}
  \left\{
    \begin{aligned}
      px-y-4&=0\\
      2x-2y-6m&=0
    \end{aligned}
  \right.
\end{equation*}
\end{document}

to get an aligned system of equations with a brace on the left. How to achieve a similar effect in ConTeXt? I tried saying \startalign[left=\{] and similar things with no effect.

Edit: thanks to Aditya's and Marco's comments below I came up with this:

\starttext
\startformula
  \startmathmatrix[left={\left\{},right={\right.},distance=0pt,align={right,left}]
    \NC px-y-4\NC{}=0\NC\NR
    \NC 2x-2y-6m\NC{}=0\NC\NR
  \stopmathmatrix
\stopformula
\stoptext

Now my question is: can this be made better? I do not like the distance=0pt and {} stuff very much (but I guess this keeps the spacing on both sides of the equation sign uniform).

Answer 1

As mentioned in the documentation Using \startalign and Display math in ConTeXt you can use the \startmathmatrix … \stopmathmatrix environment.

It makes sense to define your own environment for equation systems. This has the advantage that it is logically marked up. “This is an equation sytem” as opposed to “This is a multi-line formula with a brace at the left”. You can change the layout of the equation systems globally and it keeps the source code clean and makes it easier to read.

I would also get rid of the ugly pair of braces. However, I don't have a proper solution for the correct spacing (either wait for Aditya to tune in – he's the expert for math or ask on the mailing list).

\definemathmatrix
  [eqnsystem]
  [left={\left\{},
   right=\right.,
   distance=.3em,
   align={right, left}]

\starttext
\startformula
  \starteqnsystem
    \NC px-y-4   \NC =0 \NC\NR
    \NC 2x-2y-6m \NC =0 \NC\NR
  \stopeqnsystem
\stopformula
\stoptext