Hans Aberg
7. Juli 2015 21:11
On 7 Jul 2015, at 20:17, Wolfgang Schuster <schuster.wolfgang@gmail.com> wrote:

You can set the alignment for each column in a matrix with the align key.

FYI, the document amshelp.pdf says that AMS-LaTeX environments align, align*, and aligned, can have multiple alignments, and gives this example:
  K &\approx G * H&   i&= j+k&  B &\subset C\\
  H &\approx A_{0}*B_{0}&  i’&= j’+k’&  C &= D\cap E\\
  G &\approx \coprod_{\alpha\in A} L_{\alpha}&  i’’&=j’’+k’’& A &= D \cup E
which is typeset so that 'K &\approx G * H’ is one equation aligned on the ‘&’ with the others below, followed by 'i&= j+k’ in the next column.

So the ampersands have multiple functions here, it seems: alignment and separating columns.

Translating into ConTeXt, one might have (pseudocode):
    \NC K \NA \approx G * H \NC  i\NA= j+k \NC B \NA \subset C \NR
    \NC H \NA \approx A_{0}*B_{0} \NC   i’\NA= j’+k’ \NC   C \NA = D\cap E\NR
    \NC G \NA \approx \coprod_{\alpha\in A} L_{\alpha}
      \NC   i’’\NA =j’’+k’’ \NC  A \NA = D \cup E \NR
where I have introduce a symbol \NA for alignment.

You should google for mathalign.pdf which explains and shows examples for the matrix, cases etc. environments.

To get the same result as your LaTeX example you can use the m key for \startalign.


    \NC K \NC \approx G * H                            \NC  i   \NC = j+k     \NC B \NC \subset C  \NR
    \NC H \NC \approx A_{0}*B_{0}                      \NC  i'  \NC = j'+k'   \NC C \NC = D\cap E  \NR
    \NC G \NC \approx \coprod_{\alpha\in A} L_{\alpha} \NC  i'' \NC  =j''+k'' \NC A \NC = D \cup E \NR