[Xy-pic] \newdir
Ross Moore
ross.moore at mq.edu.au
Mon Mar 27 00:58:27 CEST 2017
Hi Michael,
> On 26 Mar 2017, at 23:40, Michael Barr <barr at math.mcgill.ca> wrote:
>
> I got an email from a user that said:
>
> in xybarr.tex the line
>
> \newdir_{ (}{{ }*!/-.5em/@_{(}}%
>
> is missing, necessary to make certain hooked arrows with extra space
> work correctly.
We’d need to see an example of just what he means.
>
> He called it a bug. Now I never claimed to put every arrow type into diagxy (= xybarr, not my name for it) and I admit to understanding \newdir much less well than I would like to, but I cannot get his macro to work.
> In fact, if I try to compile a diagram not even using his macro, it stops on a missing number error.
I don’t get that error at all.
Look at the following comparison, when _{ (} is defined,
and try it for yourself when not.
>> \documentclass{article}
>> \usepackage{matrix}{xy}
>> \newdir_{ (}{{ }*!/-.5em/@_{(}}
>>
>> \begin{document}
>> \[
>> \xymatrix{A & B\\ C\ar@{^(->}[ur] & D }\qquad
>> \xymatrix{A & B\\ C\ar@{_(->}[ur] & D }\qquad
>> \xymatrix{A & B\\ C\ar@{{ (}->}[ur] & D }\qquad
>> \xymatrix{A & B\\ C\ar@{_{ (}->}[ur] & D }
>> \]
>>
>> \end{document}
> On the other hand, if I comment out his macro then
>
> \documentclass{article}
> \usepackage[barr]{xy}
>
>
> % \newdir_{ (}{{ }*!/-.5em/@_{(}}%
>
> \begin{document}
>
>
> $$\bfig
> \Square/ (->`>`>`>/[A`B`C`D;```]
> \efig$$
>
> \end{document}
>
> compiles fine and produces a hooked arrow. There is a \newdir{ (}{{ }*!/-.5em/@^{(}}.
Yes, but it hooks the wrong way.
> Can anyone tell me what is going on here. What does the underscore in his \newdir mean anyway?
According to §6.1 on p.16 of xyrefer.pdf
the _ is a ⟨variant⟩ specifier, which can modify directionals, as is done here.
So I’d say the suggestion here is a good one, as it just
adds a variant version of something that you already have.
>
> Michael
>
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Hope this helps
Ross
Dr Ross Moore
Mathematics Dept | 12 Wally’s Walk, 734
Macquarie University, NSW 2109, Australia
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M:+61 407 288 255 | E: ross.moore at mq.edu.au
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