LMTX, mathcases and noalign

[Jean-Philippe Rey <jean-philippe.rey@centralesupelec.fr>]

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Dear list,

I am trying to switch from MKIV to LMTX. I've just found a discrepancy with the following code which puts space between two lines in a math alignment. This minimum breaking example uses \startcases, but the same problem arises with other alignment macros.

\starttext
\startformula
\startcases
\NC 1 \NC if not null \NR
\noalign{\vskip2ex}
\NC 0 \NC if null \NR
\stopcases
\stopformula
\stoptext

This snippet works fine with MKIV but breaks in LMTX (see attached log file). Is this a bug in LMTX or is there another way to insert space between two lines?

I've already tried different other solutions, but none seems really appropriate:

- \intertext produces a vertical space of at least 3 lines and I haven't been able to make it smaller;

- adding an empty line (\NC \NR) produces a smaller space but I am unable to reduce its height below a minimum value (roughly a line);

- adding a \vrule to the above or below line works fine but it needs some calculation depending on the content of the line.

Thank you for your help,

-- 
Jean-Philippe Rey
jean-philippe.rey@centralesupelec.fr
91192 Gif-sur-Yvette Cedex - France
Empreinte PGP : 807A 5B2C 69E4 D4B5 783A 428A 1B5E E83E 261B BF51

[-- Attachment #2: noalign-mfe.log --]
[-- Type: application/octet-stream, Size: 1797 bytes --]

open source     > level 1, order 1, name 'cont-yes.mkiv'
system          > 
system          > ConTeXt  ver: 2020.11.08 12:42 LMTX  fmt: 2020.11.13  int: english/english
system          > 
system          > 'cont-new.mkiv' loaded
open source     > level 2, order 2, name '/Users/jprey/Applications/ConTeXt/2020-11-09/tex/texmf-context/tex/context/base/mkiv/cont-new.mkiv'
system          > beware: some patches loaded from cont-new.mkiv
close source    > level 2, order 2, name '/Users/jprey/Applications/ConTeXt/2020-11-09/tex/texmf-context/tex/context/base/mkiv/cont-new.mkiv'
system          > files > jobname 'noalign-mfe', input './noalign-mfe', result 'noalign-mfe'
fonts           > latin modern fonts are not preloaded
languages       > language 'en' is active
open source     > level 2, order 3, name './noalign-mfe.tex'
fonts           > preloading latin modern fonts (second stage)
fonts           > 'fallback modern-designsize rm 12pt' is loaded

tex error       > tex error on line 5 in file ./noalign-mfe.tex: Misplaced \crcr


<macro> \math_cases_NR [#1][#2]->\strc_formulas_place_number_nested {#1}{#2}\crcr 
    
<macro> \dodirectdoubleempty ...\expandafter \syst_helpers_direct_double_empty_one_yes \else \expandafter \syst_helpers_direct_double_empty_one_nop \fi #1
    #2
<template> \stopimath 
    \endtemplate 

<line 4.5> \noalign
    {\vskip2ex}


 1     \starttext
 2     \startformula
 3     \startcases
 4     \NC 1 \NC if not null \NR
 5 >>  \noalign{\vskip2ex}
 6     \NC 0 \NC if null \NR
 7     \stopcases
 8     \stopformula
 9     \stoptext
10     


I can't figure out why you would want to use a tab mark or \cr or \span just
now. If something like a right brace up above has ended a previous alignment
prematurely, you're probably due for more error messages.



[-- Attachment #3: noalign-mfe-error.log --]
[-- Type: application/octet-stream, Size: 790 bytes --]

return {
 ["errortype"]=0,
 ["filename"]="./noalign-mfe.tex",
 ["lastcontext"]="\n<macro> \\math_cases_NR [#1][#2]->\\strc_formulas_place_number_nested {#1}{#2}\\crcr \n    \n<macro> \\dodirectdoubleempty ...\\expandafter \\syst_helpers_direct_double_empty_one_yes \\else \\expandafter \\syst_helpers_direct_double_empty_one_nop \\fi #1\n    #2\n<template> \\stopimath \n    \\endtemplate \n\n<line 4.5> \\noalign\n    {\\vskip2ex}",
 ["lastluaerror"]="?",
 ["lasttexerror"]="Misplaced \\crcr",
 ["lasttexhelp"]="I can't figure out why you would want to use a tab mark or \\cr or \\span just\nnow. If something like a right brace up above has ended a previous alignment\nprematurely, you're probably due for more error messages.",
 ["linenumber"]=5,
 ["offset"]=10,
 ["skiplinenumber"]=5,
}

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