# [NTG-context] underbrace under matrix

Mikael Sundqvist mickep at gmail.com
Fri Aug 5 07:03:28 CEST 2022

On Fri, Aug 5, 2022 at 2:01 AM Jethro Djan via ntg-context
<ntg-context at ntg.nl> wrote:
>
> Hello,
>
> I want to get underbraces under matrices in a math alignment environment. I’ve reproduced my problem here:
>
>  \definemathmatrix
>    [pmatrix]
>    [left={\left(\,},right={\,\right)}]
>
>  \starttext
>  \placeformula[-]\startformula\startmathalignment
>    \NC\
>    A \NC=\underbrace{
>    \startpmatrix
>      \NC 5\NC 5\NR
>      \NC -1\NC 7\NR
>    \stoppmatrix}\NR
>    \NC\NC=\underbrace{
>    \startpmatrix
>      \NC 2\NC 1\NR
>      \NC 4\NC 2\NR
>   \stoppmatrix}\NR
>  \stopmathalignment\stopformula
>   \stoptext
>
> How can I achieve this?
>
> Jethro

Hi Jethro,

Temporary workaround: use the simplecommand.

\definemathmatrix[pmatrix][matrix:parentheses][
simplecommand=pmatrix,
]

\starttext
% \placeformula[-]
\startformula
\startalign
\NC A \NC = \underbrace{\pmatrix{5,5;-1,7}}_{B} \NR
\NC\NC = \underbrace{\pmatrix{2,1;4,2}}_{C} \NR
\stopalign
\stopformula

% \placeformula[-]
\startformula
A \alignhere=
\underbrace{\pmatrix{5,5;-1,7}}_{B}
\breakhere
=
\underbrace{\pmatrix{2,1;4,2}}_{C}
\stopformula
\stoptext

But the code you were using should in principle also work.

/Mikael