Hi Henri,
Thanks for your suggestions, they are very instructive.
However, my request is not a smart way of displaying matrices
but to know why \bmatrix and \vmatrix are not provided
in core part of ConTeXt although \pmatrix is provided already
in math-pln.mkiv

About matrices, I first found commands in your first email in
http://dl.contextgarden.net/myway/context-latex-math.pdf
(like \startpmatrix \NC A\NC B\NR \NC C\NC D\NR\stoppmatrix)
and then browsing ma-cb-en.pdf I noticed another command
like \pmatrix{A&B\cr C&D\cr}.
Now by your email, I know a command \pmatrix{A, B; C, D}

One might say ConTeXt is flexible but I've an impression
that ConTeXt is in a state of confusion/disorder.

I think it is better if a standard command is provided
by core ConTeXt or by a module etc.

Or is it ConTeXt way that each user defines his/her own commands
in setup area and uses them in text area?
I'm afraid consistency and/or portability is lost in such scenario.

BTW, I constantly convert Beamer documents into ConTeXt's
simpleslide documents recently and it is very convenient
if I can use \pmatrix{a&b\cr c&d\cr} style because it is similar
to LaTeX documents.

2019年7月3日(水) 15:42 Henri Menke <henrimenke@gmail.com>:

>
>
> On 3/07/19 6:00 PM, Atsuhito Kohda wrote:
> > I've used LaTeX quite a long time but recently I begin to use ConTeXt
> too.
> > So I'm very sorry if the following is well-known issue.
> >
> > I find an example of \pmatrix in p.21 of "ConTeXt Mark IV an excursion"
> > (ma-cb-en.pdf).  And I notice it is defined in
> > /usr/share/texmf/tex/context/base/mkiv/math-pln.mkiv (in Debian).
> > But it seems \bmatrix, \vmatrix are not defined yet.
> > Is there any reason why they are not defined?
> > Similar commands or environments \begin{bmatrix}...\end{bmatrix},
> > \begin{vmatrix}...\end{vmatrix} are very often used in mathematical
> > LaTeX documents.
> > It is very useful if we can use \bmatrix and \vmatrix in ConTeXt
> > documents, so please add
> > \unexpanded\def\bmatrix#1%
> >   {\left[\matrix{#1}\right]}
> > \unexpanded\def\vmatrix#1%
> >   {\left|\matrix{#1}\right|}
> > in math-pln.mkiv or somewhere.
>
> Ignore my other message, this is even better:
>
> \definemathmatrix
>   [pmatrix]
>   [matrix:parentheses]
>   [simplecommand=pmatrix]
>
> \definemathmatrix
>   [bmatrix]
>   [matrix:brackets]
>   [simplecommand=bmatrix]
>
> \definemathmatrix
>   [vmatrix]
>   [matrix:bars]
>   [simplecommand=vmatrix]
>
> \definemathmatrix
>   [Vmatrix]
>   [left={\left\lVert\mskip\thinmuskip},
>    right={\mskip\thinmuskip\right\rVert},
>    align=middle,
>    simplecommand=Vmatrix]
>
> \starttext
>
> \startformula
>     \startpmatrix
>         \NC A \NC B \NR
>         \NC C \NC D \NR
>     \stoppmatrix
>     \quad
>     \startbmatrix
>         \NC A \NC B \NR
>         \NC C \NC D \NR
>     \stopbmatrix
>     \quad
>     \startvmatrix
>         \NC A \NC B \NR
>         \NC C \NC D \NR
>     \stopvmatrix
>     \quad
>     \startVmatrix
>         \NC A \NC B \NR
>         \NC C \NC D \NR
>     \stopVmatrix
> \stopformula
>
> \startformula
>     \pmatrix{A, B; C, D}
>     \quad
>     \bmatrix{A, B; C, D}
>     \quad
>     \vmatrix{A, B; C, D}
>     \quad
>     \Vmatrix{A, B; C, D}
> \stopformula
>
> \stoptext
>
> >
> > By the way, I think it is critical to set
> > \setupmathematics[ampersand=normal]
> > to use \matrix above but I can't find this setting in ma-cb-en.pdf
> > It is great if this is added in  ma-cb-en.pdf
> >
> >
> >
> ___________________________________________________________________________________
> > If your question is of interest to others as well, please add an entry
> to the Wiki!
> >
> > maillist : ntg-context@ntg.nl /
> http://www.ntg.nl/mailman/listinfo/ntg-context
> > webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
> > archive  : https://bitbucket.org/phg/context-mirror/commits/
> > wiki     : http://contextgarden.net
> >
> ___________________________________________________________________________________
> >
>
>
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to
> the Wiki!
>
> maillist : ntg-context@ntg.nl /
> http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
> archive  : https://bitbucket.org/phg/context-mirror/commits/
> wiki     : http://contextgarden.net
>
> ___________________________________________________________________________________
>