See if this way suits you.
\definemathmatrix[bmatrix]
  [matrix:brackets]
  [simplecommand=bmatrix]
\starttext
$ a \rightarrow
  \bmatrix{1, \hfill 2, 3, \hfill 4;
           2, \hfill 1, 4, \hfill 3;
           3,-4, 1,-2;
           4,-3, 2,-1} $
\stoptext

Bruce Horrocks via ntg-context <ntg-context@ntg.nl> 於 2023年2月27日 週一
上午8:56寫道：

> I'm using the following MWE to produce a matrix:
>
> \definemathmatrix[bmatrix]
>   [matrix:brackets]
>   [simplecommand=bmatrix]
> \starttext
> $ a \rightarrow
>   \bmatrix{1, 2, 3, 4;
>            2, 1, 4, 3;
>            3,-4, 1,-2;
>            4,-3, 2,-1} $
> \stoptext
>
> The columns with negative numbers in are centred and I would rather have
> them right-aligned so that the digits stack up above each other and the
> negative signs stick out to the left, so to speak. Is there an easy way to
> achieve this?
>
> —
> Bruce Horrocks
> Hampshire, UK
>
>
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