[Coin-discuss] modeling with GNU MathProg

[Alan King]

Hi Brady,

Thanks for sending this around.  It's great to have an opensource version 
of AMPL.

Would appreciate any thoughts out there on structuring interfaces between 
modeling methods and solver methods. 

For Stochastic Modeling Interface, we have to build labeling structures 
and associate them with LPs.  As a starter, I have drafted a simple 
version of a label object (implemented as a multimap) that can be 
"attached" to the OSI to facilitate referencing rows and columns. 

At first glance, label information really belongs to the modeling method 
side.  But specialized solver methods (eg decomposition, etc) need fast 
ways to access substructures.  These can be identified through accessing 
model information and then storing them in ways suited to the method. 

Maybe we should build a "model" class (OMI?) that has this function of 
communicating between modeling languages and solvers. 

Alan

Alan King
Mathematical Sciences, IBM Research
http://www.research.ibm.com/
http://www.research.ibm.com/people/k/kingaj/

University Relations: University of Washington
http://www.washington.edu
http://www.ibm.com/university




Brady Hunsaker <hunsaker at isye.gatech.edu>
Sent by: coin-discuss-admin at www-124.southbury.usf.ibm.com
05/17/2003 08:21 PM
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        Subject:        [Coin-discuss] modeling with GNU MathProg


The most recent release of GLPK (4.0) includes a parser for the
modeling language GNU MathProg.  It's not exactly a new language,
since it's a subset of AMPL.  It contains all of the basic
functionality of AMPL as far as I can tell, excluding things like
loops, for example.  So now there is an open-source way to process
many AMPL models.

Better yet, the parser provides its own API, although you have to look
into the source code for documentation (the documentation there is
reasonably good).

The attached tarball contains a function that uses this API to read a
model instance into an OsiSolverInterface object.  It needs to link
against the GLPK 4.0 library as well as whatever OSI libraries are
being used.  I included an example which reads in a model and solves
it using CLP.

I thought this was important enough to get such a function out there
quickly.  However, I'm writing my dissertation right now, so I won't
have time to do much more in the near future.

I'm hoping that someone else will be interested enough to take on the
task of better integrating this into OSI.  As I see it there are two
main issues:

1. Currently OSI does not provide an easy way to identify rows or
columns other than by index.  This is an issue since it's not
obvious which model constraints or variables will get which
number.  My current implementation isn't really that useful because
of this.

2. What is the best way to include the parser?  That is, where can we
include this or a similar function in COIN-OR?  Right now I'm
linking against the GLPK library, which requires that the user
install GLPK.  It would be possible to create a stand-alone parser
for COIN-OR by extracting the necessary parts of GLPK, but this
would have to be licensed under the GPL (I don't think that's a bad
thing, but we probably can't do it until we're incorporated, if
then).  Maybe there are other possibilities.

I'm happy to talk about this, though I can't justify much more coding
right now.

Brady

----------------
Brady Hunsaker
Georgia Institute of Technology
Program in Algorithms, Combinatorics, and Optimization
School of Industrial and Systems Engineering

E-mail address:   hunsaker at isye.gatech.edu



#### ReadGNUMathProg.tar.gz has been removed from this note on May 19, 
2003 by Alan King
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