> Hans Aberg <mailto:haberg-1@telia.com>
> 6. Juli 2015 11:03
> Smallmatrix from AMS-TeX is not implemented in ConTeXt (Tex Live 
> 2015), though crossed out in m-newmat.tex. I found this old post:
> http://www.ntg.nl/pipermail/ntg-context/2005/013146.html

You can create your own matrix environment for inline use:

\definemathmatrix
   [smallmatrix]
   [left=\Big(,
    right=\Big),
    style=\scriptstyle,
    strut=0.7,
    distance=.25em]

\starttext

This is a example \m{ \startsmallmatrix \NC a \NC b \NR \NC c \NC d \NR 
\stopsmallmatrix } for a smallmatrix environment.

\stoptext

Wolfgang