[Help-glpk] [annonce] ffi-glpk extension demonstrator for jruby

[Diamantini Maurice]

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.

## ./