nested environment with a star

Question

I want to redefine an environment that include the environment alignat*.

I discovered that I can't do that :

\newenvironment{variables}
{  \paragraph{Variables :}

\begin{alignat*}{2} }
{  \end{endalignat*} }

so the solution I found is to use the command \alignat but this way, the equations are numebered and I won't.

\newenvironment{variables}
{  \paragraph{Variables :}

\alignat*{2} }
{  \endalignat* }

So how can I do to include \alignat* in my new environment keeping the star ?

David Carlisle · Answer 1 · 2014-10-11T11:01:49.393

2

\csname endalignat*\endcsname expands to the command \endalignat* that you can't normally type. So \foo here is a helper macro that makes the environment definition that you intended except that the command names are passed as arguments #1 and #2, then \expandafter is used to make the command names socthe construction is the same as

\foo{\alignedat*}{\endalignedat*}

but with * interpreted as part of the command name, as if it were a letter.

\documentclass{article}

\usepackage{amsmath}



\def\foo#1#2{%
\newenvironment{variables}
{\paragraph{Variables :}
#1{2}}
{#2}}
\expandafter\foo
  \csname alignat*\expandafter\endcsname
  \csname endalignat*\endcsname

\begin{document}

\begin{variables}
a&b\\
aaa&bbb
\end{variables}

\end{document}

edited Oct 11 '14 at 11:01

answered Oct 11 '14 at 10:09

David Carlisle

757,742

Can you explain how does it work please ? – Saroupille Oct 11 '14 at 10:18
@Saroupille added some notes:-) – David Carlisle Oct 11 '14 at 11:02
Ok thanks ! I just don't understand the \expandafter command. If we don't use it, what happens ? – Saroupille Oct 11 '14 at 11:11
@Saroupilleif you don't use it then it doesn't work:-) there is probably an answer on site explaining \expandafter I'll post a link – David Carlisle Oct 11 '14 at 11:14
@Saroupille put \expandafter in the search box, lots of answers, perhaps start with http://tex.stackexchange.com/questions/161064/how-does-your-mind-bend-expandafter-to-its-will – David Carlisle Oct 11 '14 at 11:16
By the way, instead of \csname endalignat*\endcsname one can use more simply \endalign. – egreg Oct 11 '14 at 22:25
1

@egreg yes, I know, but I thought that would look even more weird (and is specific to those environments:-) – David Carlisle Oct 11 '14 at 22:34

score 2 · Accepted Answer · answered Oct 11 '14 at 11:53

2

Why define \foo? May be I missed something but you can inglude \csname inside the definitions

\newenvironment{variables}
  {\paragraph{Variables :}
   \csname alignat*\endcsname{2}}
  {\csname endalignat*\endcsname}

answered Oct 11 '14 at 11:53

Manuel

27,118

hmm actually you can (so +1:-) although it's less efficient in both space and time, although I was thinking when I wrote it that the environment detection trickery that the ams alignments do would require the command token exposed, but I think you're right that isn't actually needed here. – David Carlisle Oct 11 '14 at 22:38
@DavidCarlisle I think this has been the first tick I've borrowed from someone. – Manuel Oct 12 '14 at 13:22
Beware, keep doing that and you'll turn into egreg, you wouldn't want that:-) – David Carlisle Oct 12 '14 at 14:49

nested environment with a star

2 Answers2