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Re: Getting an array into a C program through mathlink

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  • Subject: [mg130333] Re: Getting an array into a C program through mathlink
  • From: "John D. Hendrickson and Sara Darnell" <johnandsara2 at cox.net>
  • Date: Wed, 3 Apr 2013 04:11:02 -0400 (EDT)
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  • Reply-to: johnandsara2 at cox.net

Ok I think you asked for a little more info about why mathlink which 
seems fine on developer's machine might not be fine elsewhere.

Why is because to work mathlink needs to link against OS libraries 
which change.

http://reference.wolfram.com/mathematica/tutorial/MathLinkDeveloperGuide-Unix.html#725481284

clearly says it is library hooked and versional to specific libraries.

http://support.wolfram.com/search/?query=mathlink&lang=en&noImg=1&submit.x=0&submit.y=0

are some problem reports of:

LinkConnect::"linkc": "\!\(\[LeftSkeleton] 1 \[RightSkeleton]\) is 
dead; attempt to connect failed."

(there were many unsure if wr has removed them.  or search Google and 
find some.  it's hard to believe you looked hard if you can't find any.)

For example I have Mathematix Version zzz.  I later upgrade Linux. 
Mathlink is now broken.  I may be able to run simple pre-compiled ones 
(unlikely to be available for my exact linux disto) but most won't 
work because the libs have changed or they are for a different linux 
distro.  You'd think "just recompile mathlink apps".  NO.

To resolve this I need to run Mathematica and any mathlink apps in a 
chroot of a previous Linux version.  Compilation of other people's 
mathlink apps would also have to be done in the chroot - which won't 
work for newer mathlink apps.  Too much effort.

You'd think I can just compile against older libs: surprise that works 
at compile time but not run-time since libML.a is loaded accessed 
through the newer libs and it is older: IT WON'T EVER WORK.

My other choice is to buy new mathematica.  But if I had any mathlink 
apps I needed I'd have to rewrite them since they won't compile with 
the new linux libs / environment.  This also requires a new computer. 
$$  And how long is it until it's all broken again?

(obviously upgrading Mathematica is better if you have time and money 
for the "upgrade escapade")

(Note I mean Linux distribution, the linux kernel isn't usually 
involved.  unlike the old days: often binaries today often won't work 
when copied from one distro to another, due to lib variations they 
keep uploading)

Obviously there's another answer: wolfram releases a different 
mathlink that doesn't rely on lib offsets runtime :)  I won't go into 
it but I know what breaks it.

--------------------------------

John Fultz wrote:
> That's an interesting observation, but I can't say it matches my own experience.  I've found MathLink to be remarkably compatible across major version number changes of Mathematica, and to be generally robust.  It is the only way the FE and the kernel communicate with each other (not to mention other lesser components of the system), and the nature of that connection is not simple; I would say it uses a majority of the features that MathLink has to offer.
> 
> It's not clear to me exactly what you're referring to as "Wolfram problem reports".  But I'd certainly be interested in knowing about any issues that you or anyone else may be experiencing with MathLink.
> 
> John Fultz
> jfultz at wolfram.com
> User Interface Group
> Wolfram Research, Inc.
> 
> 
> 
> On Apr 1, 2013, at 12:00 AM, debguy <johnandsara2 at cox.net> wrote:
> 
>> my advice is to avoid mathlink because library issues cause
>> compatibility problems (see Wolfram problem reports).  ie after or
>> without upgrade it's broken for someone trying to use.
>>
>> if you can accept fast but not fastest results I suggest this:
>>
>> to use "exec" in C to call math binary with piped commands (we're
>> talking text input output) and use Put to get what into a file (can
>> even be forked, run in background, doing it that way).  then your
>> application reads file when done (fread is fast, maybe not fast as
>> direct read from mathlink).
>>
>> most tasks can be done without ever using C.  doing some special
>> graphics or something?
>>
> 
> 




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