[dev-context] My way on matharrows

[Hans Hagen]

Taco Hoekwater wrote:
> Aditya Mahajan wrote:
>   
>> Hi,
>>
>>  I am attaching myway on using matharrow. Are there any suggestions 
>> before I release it to public?
>>
>> I found some surprises while making this my way.
>>
>> 1. Somewhere along the line of development, \xrightarrow{text} changed 
>> to placing text at the bottom of the arrow (rather than the top as in 
>> amstex). This is not a bug, just something that works differently. 
>> Should this be changed? These arrow definitions are pretty new, so I do 
>> not think that a change at this stage will effect too many users. It may 
>> not be possible to change later for compatibility reasons.
>>     
>
> In the interest of porting stuff from amstex, changing the behaviour is
> probably better.
>   
\def\dodoxmtharrow[#1,#2,#3][#4,#5,#6][#7]#8#9% [3] is the optional arg
  {\ifx#2\empty
     \ifsecondargument
       \mathrel{\domthxarrsingle{#7}{#1}{#4}{#8}{#9}}%
     \else
       \mathrel{\domthxarrsingle{#7}{#1}{#4}{}{#8}}%
     \fi
   \else
     \ifsecondargument
       \mathrel{\domthxarrdouble{#7}{#1}{#2}{#4}{#5}{#8}{#9}}%
     \else
       \mathrel{\domthxarrdouble{#7}{#1}{#2}{#4}{#5}{}{#8}}%
     \fi
   \fi}
>   
>> 2. Something goes wrong with palatino (used by mag-01). Have a look at 
>> the \xmapsto and \xrightleftharpoons and \xleftrightharpoons in the pdf. 
>> \xmapsto can be corrected by changing its defintion to
>>
>> \definematharrow [xmapsto]            [3599] [\mapstofill]
>>
>> Basically, providing a bit more cusion on the left, so that the middle 
>> \relbar not overlap the \mapstochar.
>>
>> Should this definition go to math-ext.tex or to something specific to 
>> palatino. I have not tested with other fonts, but what is the general 
>> strategy when definitions differ for different fonts?
>>     
>
> something should be possible with mathcollections, I guess?
> (Hans knows this better then I do)
>
>   
it's font related, not collection related; the problem with these things 
is that in context we want to deal with mixed math font usage so we need 
to figure out a clever way
>> I could not correct leftrightharpoons. Why does this not work?
>>
>> \definematharrow [xleftrightharpoons] [3395,3359] 
>> [\leftharpoonupfill,\rightharpoondownfill]
>>     
>
> Because the current definition of dodoxmtharrow does not like it
> when the second arg starts with two identical digits. Changing
> it to this fixes the problem:
>
>    \def\dodoxmtharrow[#1,#2,#3][#4,#5,#6][#7]#8#9%
>    {\edef\tempa{#2}\ifx\tempa\empty %TH changed line
>       \mathrel{\domthxarrsingle{#7}{#1}{#4}{#8}{#9}}%
>     \else
>       \mathrel{\domthxarrdouble{#7}{#1}{#2}{#4}{#5}{#8}{#9}}%
>     \fi}
>
>   
ok, so we get

\def\dodoxmtharrow[#1,#2,#3][#4,#5,#6][#7]#8#9% [3] is the optional arg
  {\edef\!!string{#2}%
   \ifx\!!stringa\empty
     \ifsecondargument
       \mathrel{\domthxarrsingle{#7}{#1}{#4}{#8}{#9}}%
     \else
       \mathrel{\domthxarrsingle{#7}{#1}{#4}{}{#8}}%
     \fi
   \else
     \ifsecondargument
       \mathrel{\domthxarrdouble{#7}{#1}{#2}{#4}{#5}{#8}{#9}}%
     \else
       \mathrel{\domthxarrdouble{#7}{#1}{#2}{#4}{#5}{}{#8}}%
     \fi
   \fi}

Hans

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