On Fri, 23 May 2014, Matthias Weber wrote:

> Dear All,
>
> I would like to define a command that expands
>
> \vector{2,4} % or vector[2,4] if that’s easier
>
> to
>
> \startpmatrix
> \NC 2 \NR
> \NC 4 \NR
> \stoppmatrix
>
> and more generally
>
> \vector{2,4,1,7}
>
> to
>
> \startpmatrix
> \NC 2 \NR
> \NC 4 \NR
> \NC 1 \NR
> \NC 7 \NR
> \stoppmatrix
>
> Any hints how to achieve this?

Surprisingly, this is not as simple as it may seem at first glance. Some 
time ago, I had written a module to achieve this. See attached. The usage 
is:

\usemodule[simplematrix]

\definesimplematrix[MATRIX][fence=bracket]

(any predefined math-fence will work) and then:

\MATRIX{1,2,3} for row vectors and \MATRIX{1;2;3} for column vectors, and 
\MATRIX{1,2,3; 4,5,6} for matrices.

You can use \definesimplematrix[...][distance=..., align=...] to influence 
the distance and align keys of mathmatrix.

Aditya