Forum: JRuby [annonce] ffi-glpk extension demonstrator for jruby

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Diamantini Maurice (Guest)
on 2009-01-27 22:17
(Received via mailing list)
Bonjour à tous,

I'm trying to test a new extension provide with jruby which allows
to write a binding for a C library directly in ruby without
writing a C line of code.
This (ffi) extension is now part of the standard Jruby version.
That allows to use mixing of java library (like choco constraint
solver), C extensions (like glpk) directly in (j)ruby code.

As Pierre asked (on the Glpk list) for a java or other binding
for Glpk, I write this "pseudo-annonce" although ffi-glpk is just
a demonstrator for now.
But it allows to write the glpk documentation minimal example
in **full (j)ruby** code!

The demonstrator is available at :
     http://www.ensta.fr/~diam/ruby/online/pub/

The code provided is the mimimum for writing the glpk doc mini
example in ruby.

Hope this help,
-- Maurice Diamantini

Here is the README :
==============================================================
## what is it

This directory contains a test exemple to validate Glpk interface to
(J)Ruby
thanks to the new ffi Ruby package.

     - Glpk is the Gnu Library tookit for Linear Programming written
in C
       by Andrew Makhorin,
          http://www.gnu.org/software/glpk/

     - Ruby is a wonderfull true objet oriented programming scripting
language
       written in C

     - JRuby is a Ruby (100% compatible) version written in Java and
fully
       supported by Sun. It is also fully integrated with the java
world and is
       as fast as the new native Ruby-1.9 version
         http://jruby.org/

     - FFI is a new package which allow to write 100% Ruby interface
to C
       library!! FFI is currently fully integrated with JRuby language.
       and can be installed for Ruby native language.
         http://kenai.com/projects/ruby-ffi/pages/Home

## The provided exemple allow to solve the following problem :

     max z = 10x1 + 6x2 + 4x3
     s.c.
        x1 +  x2 +  x3 <= 100
      10x1 + 4x2 + 5x3 <= 600
       2x1 + 2x2 + 6x3 <= 300

       x1 >= 0
       x2 >= 0
       x3 >= 0


This directory contains :
- a file "miniglpk.c" which is exactly the glpk exemple provide with
the glpk
   documentation.
   You should be able to test this programme to make sure glpk is
installed on
   your system, but a compilator is not required for using glpk from
(J)ruby

- a file "ffi-glpk.rb" wich contains the minimum for writing the low
level
   API used in the tutorial example,

- the file "mini_glpk.rb" which is the the ruby version of the tutorial.


## Execution of the test the C version

For compiling and running the C exemple, you should set two environment
variables :

- GLPK_LIB should be set the path were the library file libglpk.so or
   libglpk.dylib is located,
   For sample
     export GLPK_LIB=/usr/local/lib

- GLPK_INCLUDE should be set the path were the library file glpk.h
   is located
   For sample
     export GLPK_LIB=/usr/local/lib

Then compile by:
     gcc -I$GLPK_INCLUDE -L$GLPK_LIB -l glpk -o mini_glpk mini_glpk.c
and run by:
     ./mini_glpk
The following result should appear:

     *     0: obj =   0.000000000e+00  infeas =  0.000e+00 (0)
     *     2: obj =   7.333333333e+02  infeas =  0.000e+00 (0)
     OPTIMAL SOLUTION FOUND
     z = 733.333; x1 = 33.3333; x2 = 66.6667; x3 = 0


## Execution the jruby test

You should have the last jruby version (jruby-1.6) which contains
FFI out of the box, or ruby and install ffi with
    gem install ffi (not tested)

Also, the glpk lib should be discover aumoticaly on osx leopard or
recent
linux distrib, but for now, you can specify the path path (i.e. bu
using the  previous GLPK_LIB variable.
See the start "ffi-glpk.rb" if you have problems

    then run
    ./mini_glpk.rb

It's all !

## Remark about the "ffi-glpk.rb" interface file

This kind of file could become the low level interface to the glpk
library.

It seems that the FFI community converge to the idea that there should
be one standard **low** level interface to a C library. It is essentialy
a sort of mapping of the include file and should be easy to maintain
(ideally automically generated from the include file).

Then it could exist several higher level API to make this interface more
Object Oriented ou more Ruby frendly.

## ./



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Charles Oliver N. (Guest)
on 2009-01-28 22:16
(Received via mailing list)
Diamantini Maurice wrote:
> for Glpk, I write this "pseudo-annonce" although ffi-glpk is just
> a demonstrator for now.
> But it allows to write the glpk documentation minimal example
> in **full (j)ruby** code!

Wow, I missed this email before, but it sounds great! A very practical
use of FFI to be sure. Will you release this as a gem?

- Charlie

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Maurice Diamantini (Guest)
on 2009-01-28 23:26
(Received via mailing list)
2009/1/28 Charles Oliver N. <removed_email_address@domain.invalid>:
>>
>> As Pierre asked (on the Glpk list) for a java or other binding
>> for Glpk, I write this "pseudo-announce" although ffi-glpk is just
>> a demonstrator for now.
>> But it allows to write the glpk documentation minimal example
>> in **full (j)ruby** code!
>
> Wow, I missed this email before, but it sounds great! A very practical use
> of FFI to be sure. Will you release this as a gem?

Sorry, no (I've never build gem yet).

Also, It's just a demonstrator which implement just the few API that
allowed me to write the little glpk sample.
So I should first build a more realistic example (which use more
glpk feature), then build build a more OO shell over the ffi-glpk to
make it more higher level.

But it already shows how easy it is to call a scientific C library
directly from jruby.

However I don't use glpk very much and I hope a regular user
would be more able to do that. Also, most part of ffi-glpk is very
similar to the glpk.h file (which is big with many feature !).

So It should be a mean to automatically generate the big part of
ffi-glpk,
perhaps with some reformatting of the glpk.h.

-- Maurice

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